Over 50 million Apple iPods, and lots of competing digital music players, have been sold by now — as well as over a billion songs and tens of millions of videos, since legal media sales took off a few years ago.

But many folks — even some who own iPods and other players — are still confused over how legal digital music works. So here’s a quick-and-dirty guide to the digital music world, in question-and-answer form. We’ve included the questions we are asked most frequently, plus a few other topics.

What’s the difference between the Apple iPod and all the other portable music players? Some of them seem to have more features.

The main difference is that Apple has created an entire end-to-end digital media system around the iPod, and it works. In our view, and those of most other reviewers, the combination of the iPod’s design, the iTunes music software, and the iTunes Music Store, provides a superior experience to buying a player separately, using software from Microsoft, and buying music from an unaffiliated store.

As a result, the iPod, and the iTunes store, dominate the legal music world, with shares of more than 70% of the market, depending on how you measure it.

Still, players from companies like iRiver and Creative are attractive and have some features the iPod lacks, such as built-in FM radios. And music services from RealNetworks, Yahoo, Napster and others offer an interesting alternative to iTunes.

If I buy an iPod, must I buy music from Apple’s iTunes store? Conversely, can I buy music from Apple, and play it, if I don’t have an iPod?

No, and yes. You don’t have to buy a single song from Apple. You can fill an iPod entirely with music you convert from your own CDs, or which you get from unauthorized download services, or from friends. The latter two sources are probably illegal, but they are technically easy to use. In fact, most of the song files on most of the world’s iPods weren’t purchased from Apple, or anyone else. That’s because the iPod, and iTunes, can play back files in the open MP3 format, and in other non-copy-protected formats.

Conversely, you can set up an account with the iTunes Music Store and buy as many songs, videos, and other material as you like, without owning an iPod. You would simply play back your purchased media on Windows or Macintosh computers. You can play any one song on as many as five different computers. All you need is the free iTunes software, which can be downloaded from Apple’s Web site in either a Windows or Mac version.

Will songs purchased from iTunes play back on non-iPod portable players? Will songs purchased from competing services play back on iPods?

No, and no — unless you use a workaround (see next answer). At the insistence of the record labels, all songs from major label catalogs that are sold as online downloads must be encrypted to limit copying. There are two encryption formats. One is owned by Apple, and the other is owned by Microsoft. The iTunes Store uses the Apple encryption format, and most other legal download services use the Microsoft format.

Any player from any company can theoretically be enabled to use either format, but Apple refuses to license its encryption format to any competing maker of players. And Apple also refuses to incorporate the Microsoft format on iPods. The result is that songs bought from iTunes only work on iPods, while songs bought from most other legal services only work on non-iPod players.

There is one exception. A service called eMusic sells its songs in the open MP3 format, without encryption or copy-protection. Thus, these songs will play on iPods and all other portable music players. But eMusic doesn’t carry the catalogs of the major labels. It has a much smaller selection than iTunes does.

Is there any way around this? Can I legally modify or convert encrypted songs so they will work on portable players for which they weren’t intended?

Yes, but the method is clumsy, especially if you try to apply it to a large number of converted songs.

To convert songs purchased from iTunes to an open format that will play on, say, a Creative player, or in Windows Media Player software, you first must burn the songs to CD. Then, using iTunes or other music software, you re-import them from CD, turning them into open MP3 files that can be played on any player. This works fine, but it has two big downsides.

First, it can take a long time to convert, say, 500 songs this way. Second, the process strips off all the identifying data from the song files, and home-burned CDs typically aren’t recognized by the automatic song-recognition process used by iTunes and other software. So you’ll have to manually re-enter info like artist, album and song title.

Independent site iLounge has a free manual on getting the most from your iPod.

This process works the other way as well, with a big “if.” You can convert Microsoft-encrypted songs this same way, so they become MP3 files that can be played on an iPod. But the catch is that songs offered by the leading Microsoft-based services often can’t be burned to CDs. (See next answer.)

There is some software that claims to efficiently strip the encryption from copy-protected song files, turning them into MP3 files. But these programs are almost certainly illegal under recent copyright laws, and Apple and other companies constantly change the innards of their encryption formats to foil the programs.

What is the difference between Apple’s iTunes store, and competing services like Rhapsody and Napster 2.0? Does one carry more music?

Apple’s iTunes store claims to have more than three million songs licensed from the major labels and from independents. Rhapsody and Napster claim more than two million songs, and Yahoo Music Unlimited claims more than one million. So, iTunes has by far the most music. In addition, iTunes has a strong selection of videos, including 150 television series, plus tens of thousands of audio books and podcasts. Its competitors are much weaker in these non-music categories. Most have nothing at all besides music.

The main difference lies in how the services work. iTunes works like a physical record store: you buy songs or albums, paying separately for each. Songs are 99 cents each, albums are usually $9.99, and videos are typically $1.99. Apple is reportedly negotiating to sell full-length movies as well.

Rhapsody, Napster and Yahoo work on a subscription model: you pay a monthly fee, and can download an unlimited number of songs. For Rhapsody and Napster, the fee is $10 a month if you want only to store and play music on a computer, or $15 a month if you also want to play your music on a portable player. Yahoo charges less — $6.99 a month for a PC-only plan and $11.99 a month for a portable plan.

The upside of Apple’s approach is that, once you buy a song, you own it. It never expires. You can burn it to CD an unlimited number of times, and transfer it to an unlimited number of iPods. The downside is that, to fill an iPod with, say, 5,000 purchased songs, you’d have to spend $5,000.

With the subscription plans, you can fill a portable player for just a monthly fee. But there’s a huge downside: you don’t own the music, you merely rent it. If you stop making your monthly payments, all the songs you downloaded over the years will suddenly expire and become inert and unplayable on your computer and on your portable player. Also, rental songs usually can’t be burned to CD and can only be copied to a limited number of portable players. In order to burn the tunes to CD, you generally must first buy them for an individual price, just as you do on iTunes.

How do I use multiple iPods with one iTunes library on my PC, if I want different music on each iPod?

In the Preferences section of iTunes, you can set up each iPod so it synchronizes only with particular playlists, not your whole library. Just set up a playlist for each iPod, and set it up to sync only with that playlist.

Or, you can set up each iPod so it doesn’t automatically synchronize with iTunes at all, and simply works in manual mode. Then, you can manually drag different songs into each iPod.

Can I copy the songs on my iPod to my second or third computer?

At the insistence of the record labels, Apple was forced to cripple the iPod so it can’t copy music to a computer, out of the box. Copying only works from a computer to an iPod, not the other way. But there are many third-party utility programs, for both Windows and Mac, that allow copying from an iPod to a computer. One example is PodUtil, which has versions for both Mac and Windows. It’s at: www.kennettnet.co.uk/software/podutil.php.

One thing to bear in mind: you can only play any song you buy from iTunes on up to five computers, Windows or Mac. Songs in the open MP3 format can be played on an unlimited number of computers.

Can I share the music in my iTunes software with others?

Yes, within limits. You can set up iTunes on your Windows PC or Mac so that others on your computer network (but not over the Internet) can stream, or listen to, your songs, without actually moving the song file to their computer. The receiving computer must have iTunes installed, and both machines must be enabled for sharing in the Sharing section of the iTunes Preferences panel.

What can I do with an iPod, other than play music on it?

Current iPods can play videos, like TV shows. And most iPods can play audio books and podcasts. Recent models also can play back your photos as slide shows, accompanied by music and fancy transitions. And, with a $20 cable, the iPod can display videos and photos on a TV set.

But there’s a lot of other stuff buried in an iPod. The iPod can display, but not edit, your calendar and contacts and notes, synchronized from your computer. This works with Microsoft Outlook on Windows and with the Address Book and Calendar programs that come with every Mac. Current iPods also have a built-in stop watch and multi-city clock.

You can also use your iPod as a portable hard disk. It can be set up to appear as a regular hard disk on both Windows and Macintosh computers. Any space on the iPod that isn’t occupied by your music, videos, photos and so forth can be used to store any type of file you want, for backup, or for transfer among computers. You just have to plug your iPod into your computer, go to the iPod preferences tab, and check “Enable Disk Use.”

The iPod also has some built-in games. My favorite, Music Quiz, tests your knowledge of your own music. It plays a short clip of a randomly selected song from your collection, then displays five multiple-choice song titles. Your task is to select the right title in the shortest possible time, while a clock counts down the points you can win. It’s addictive.

There’s a ton more to know about digital music, and specifically, iPods. Apple has a series of iPod and iTunes tutorials at http://www.apple.com/support/ipod101/. The independent Web site iLounge (ilounge.com) is packed with tips and tutorials and even offers a free, downloadable 194-page book about the iPod, at: http://www.ilounge.com/index.php/news/comments/download-now-the-free-ipod-book-20.

• Email: MossbergSolution@wsj.com.

Great songs, like chocolate-covered strawberries, can be sampled once and adored immediately. This is good news for online digital-music stores, where anyone with an Internet connection and a buck can log on from a computer and download a new favorite tune seconds after hearing it.

Now, XM Satellite Radio Holdings Inc. is making this audio gratification even more instant. Last month, it introduced the first portable combination XM radio/MP3 player, the $400 Pioneer Inno XM2go. Anyone with this device who likes a song playing on XM can simply press a button and record the entire song onto the player. No computer is required, but you do need an XM subscription, which costs $13 a month.

The $399.99 Pioneer Inno XM2go combines portable satellite radio with a digital music player, but watch out for reception problems.

These recorded songs can’t be transferred to PCs or other players. But they can be bookmarked for purchasing online at Napster’s music store the next time the Inno is plugged into a Windows computer. This purchased version of the song can be used on computers and other devices (but not the Apple Computer Inc. iPod).

The new XM device, made by Pioneer Corp.’s Pioneer Electronics (USA) Inc., uses flash memory rather than a hard disk, and can store 50 hours of recorded XM Satellite Radio, plus about 8 hours or 150 digital songs copied from a computer. One half of the player is reserved for XM recordings, while the other half is reserved for MP3 or WMA music files. You can switch between the two modes by pressing a button.

The Inno is at the center of a lawsuit filed yesterday by members of the Recording Industry Association of America, who are challenging the legality of the device’s recording feature.

This week, we tested the portable Inno all around town. We liked the device itself, and enjoyed listening to various satellite radio stations on the go. But we were deeply disappointed with its radio reception, which failed in too many places. And we really didn’t like working with the Napster software when we synched the player with our PC. It was a hassle.

Our verdict: adding live satellite radio and the ability to record it onto a device is a good idea, and may appeal strongly to satellite radio lovers willing to pay $13 a month to subscribe. But, for people who just like music, the radio and recording features didn’t seem like reason enough for us to want to buy the Inno over, say, an iPod — especially given the downsides we encountered.

We liked the overall feel of the Inno, and it wasn’t too tough to get the hang of its buttons and functions. It measures 3.7 inches by 2.2 inches by 0.6 inches — just slightly smaller, overall, than a full-size iPod and a little bit thicker — and its 4.5-ounce weight makes it a tad lighter than a 30-gigabyte iPod. A 1.7-inch color screen on the front doesn’t take up the entire surface, and compared to an iPod’s 2.5-inch color screen, its size was more like the one on the tiny iPod Nano, a 1.5-incher.

The back and front sides of the Inno are decorated in cool gun-metal gray. Shiny black edges give it a modern feel, while its stubby antenna resembles that of a smart phone, but thicker and perfectly cylindrical. This antenna is the device’s only means of receiving radio. That’s a breakthrough, since satellite radio usually requires a large separate antenna or a car antenna. Unfortunately, we found the Inno’s little antenna was too weak.

It’s hard to overstate the reception problems that plague the Inno. We lost reception while driving through a short tunnel, walking through a row home and wandering through our office, away from the window. Even in an office with an entire wall of windows, we had to sit right next to the glass to get XM Satellite Radio reception.

Walking around downtown Washington, just a few blocks from the White House and a few miles from XM’s headquarters, the Inno constantly dropped the XM signal, even though Washington, by law, has no office buildings taller than about 12 stories. Walking just a few feet into a Starbucks killed the signal altogether. When we sat down on a bench in a small park, the reception got much better, but still wasn’t perfect. For a device that’s primarily a radio, this is a killer flaw. Of course, you can listen to the Inno’s stash of recorded music during these signal dropouts, but, when the failures are as frequent as ours were, this need to keep switching modes turns a supposedly pleasurable experience into a huge annoyance.

Optional headphones with an antenna disguised in the headpiece can be purchased for an additional $40, and these added slightly better reception, but not much.

A well-designed button on the right side of the Inno powers it on or off when pushed downward, and puts the device on hold when pushed up. Volume controls are just below this button, also on the device’s side. Three buttons line the bottom edge of the color screen — Mode, Play/Pause and Display — and four directional arrows surround an XM select button below these three.

We checked out XM’s 20 categories of music, over 170 stations altogether, by pressing the right arrow button. We paused in the Decades category to listen to “Sunshine Superman” by Donovan on the ’60s station before skipping to Hits where Daniel Powter’s catchy new pop song “Bad Day” was playing on the “Top 20 on 20″ station.

To record “Bad Day” onto our Inno, we pressed the XM button, chose Record and Record Song. A red “REC” icon appeared at the top of the screen, and went away when the song ended. In one case, we were listening to a station when a new song that we wanted to record started before we could press the right buttons. Thanks to the magic of satellite radio, recording automatically started at the song’s beginning, rather than halfway through.

If you’d like, you can schedule times for your Inno to start and stop recording, and these can be set to record on the current day, every day or on a specified date.

When listening to Elton John’s “Something About the Way You Look Tonight” on a romantic music station appropriately named “The Heart,” we opted to Bookmark the song so that it was set aside in a special category of songs for buying when we connected our Inno to our PC. An option called TuneSelect can be chosen while a song or artist is playing; from then on, a message will flash across your screen whenever that artist or song plays anywhere on XM, so you can tune in.

Before synching our Inno with our computer, we used an included CD to load XM + Napster software onto our Dell PC and typed in a special promotional code given to us by Napster for testing.

The Napster software program is confusing, to say the least. Napster offers three types of accounts: Napster Lite, music-store usage with no monthly fee that allows online listening and purchasing of songs à la carte; Napster Membership, a $9.95-a-month program allowing unlimited music downloads onto the PC — but not for transferring to a player; and Napster To Go, a $14.95 monthly membership that allows unlimited music downloading and transferring to a device.

If that doesn’t confuse you, add the fact that because Napster offers music rentals rather than just buying of songs — like iTunes — it considers purchased tracks to be different than downloaded tracks. Overall, your purchased tracks or previously owned tracks (in MP3 or WMA file format) can be transferred to the XM2go. Downloaded (not purchased) tracks can’t be transferred to the XM2go, but they can be transferred to special, more advanced devices with what’s known in techie land as DRM 10 compliance. XM plans to introduce devices with this technology in the future.

The Inno connects to a PC using a standard USB cable, but it must be simultaneously lying in its special sideways dock, which also powers the device. When the Inno is turned sideways in its cradle, its screen automatically rotates, as do its directional arrows. This cradle also has plugs for an additional included antenna and a line out, for using the Inno with a stereo system.

In Napster’s software program, our Inno was identified, as were the songs that we had recorded and bookmarked. Songs recorded from XM can’t be exported from the player, due to copyright laws. Most of the songs we had bookmarked, including Elton John’s tune, had a Download icon next to their track titles.

But instead of seeing a Buy icon next to our bookmarked tunes, we could only purchase songs by right-clicking on tracks and choosing Buy Track since our account type was designed for streaming music rather than buying it. This type of navigational confusion was abundant in the program, and users would easily and understandably be befuddled by what account type they had and what was or wasn’t included in it.

We dragged and dropped songs onto our Inno player without a problem, and they showed up in the MP3 section of the player when we started it up again. We even created playlists, right on the Inno, combining music recorded from XM stations and our own MP3s. Switching between the live XM stations and our MP3s and WMAs was easily done with the Mode button. XM estimates that the Inno’s battery will last for 15 hours in playback mode and five and a half hours in Live XM Mode.

When it’s all said and done, XM’s Inno is fun to use on the go, as long as you’re not underground or in room without windows. But its spotty reception, confusing software and monthly fee make the Inno a no-go, except for hard-core XM fans.

• Email: MossbergSolution@wsj.com

Internet radio is very cool. It allows you to listen to both traditional radio stations from all over the globe, as streamed through Web sites, and to stations that exist only on the Net. The variety of music and talk these stations offer is staggering, but there’s a problem: To listen to them, you have to be sitting in front of a computer.

Many folks would rather listen to Internet radio in rooms where their computers don’t live, or where they’d rather not lug a laptop. To do so today, you have to buy a device that transmits music from a computer to remote speakers. These include the Squeezebox from Slim Devices Inc., Netgear’s MP101 Wireless Digital Music Player and Roku’s SoundBridge M1000.

None of these devices includes its own built-in speakers. You have to attach them to your audio system, and some require you to manage software on the computer that allows them to work over your network, a tricky process.

But, this week, we tested a new Internet radio product that’s totally self-contained and requires almost no setup. It doesn’t depend on a computer to bring in Internet radio, but does the job itself, wirelessly connecting to your broadband service, just like a computer does. And it doesn’t require an external audio system. It has its own built-in subwoofer and speakers, just like a traditional radio. It even looks like a traditional radio, but it does much more.

This new product is called the SoundBridge Radio, and comes from Roku LLC. It’s due to hit store shelves in a few weeks at around $400, which includes a remote control.

By including speakers, Roku eliminates the intimidating extra step of fiddling with wires to attach the device to a separate sound system. With its own sound system, the SoundBridge Radio can also function as an alarm clock, and it can receive your local AM and FM stations over the air, in addition to Internet radio.

Roku’s SoundBridge Radio, priced at $400, includes a remote, built-in speakers and a subwoofer.

And, even though it doesn’t require a computer for radio, the SoundBridge can pull music off your computers wirelessly and play it. It can even play music stored on a SecureDigital memory card.

We rocked out all week, listening to all different types of radio stations, and concluded that the SoundBridge Radio is a decent product, but its user interface could stand some improvement.

In addition to playing roughly 100 preprogrammed Internet radio stations, the SoundBridge Radio also detects and plays music from all libraries within range of your wireless network — without having to install any special software on your Windows or Mac computer. These libraries can include content running on Apple’s iTunes, Real Networks’ Rhapsody, Windows Media Connect and Windows Media 10, as well as services like MusicMatch, Napster, MSN Music and Walmart.com.

To add your own Internet radio stations onto the SoundBridge Radio, you must use a convoluted method involving iTunes. This summer, Roku plans to upgrade its software so as to include many more preprogrammed stations on each device.

The SoundBridge Radio is black and measures 11 inches wide, 6 inches high and 6½ inches deep. Two speakers are built into its front panel, and a subwoofer is built into its rear. A horizontal display with blue-green lettering runs across the front panel, and 13 buttons are built into the top ledge, including a hard-to-miss sleep button and six numbered preset buttons. A headphone jack and SD card slot are positioned on the player’s right side.

We had no trouble setting up the SoundBridge Radio. We plugged it in, and its display screen immediately came to life, asking us a few simple questions, which we answered by pressing the Select button on an included remote. After a few seconds of waiting, we were on our way.

This text in the display screen can be adjusted to one of six different fonts; we chose the average-size type. While the smallest enabled us to see more text, it was impossible to see across the room, and the largest font had to constantly scroll to display song information. Unlike on some other devices, the remote has no built-in little screen of its own.

Navigating through the SoundBridge Radio was confusing at times. A Source menu listed the six sections of the player, including each of our share-enabled iTunes music collections, and read: Play Walt’s iMac, Play Katie’s Music, Play AM Radio, Play FM Radio, Play Internet Radio and System Configuration. The radio itself had a Source button on it that, when pressed, easily retrieved this menu, but the remote had no such button.

The remote does have a Home button (represented by a house icon), but this goes only to the main menu within the current source, not to the useful Source menu itself.

After selecting each of our music libraries, options for how to play the music appeared on the screen, such as by selecting premade playlists or by browsing through and choosing a specific artist. We played a few songs from each of our iTunes libraries, including Billy Joel and Coldplay, and were impressed by the sound.

Music bought on Apple’s iTunes Music Store will not play on the SoundBridge Radio because of Apple’s refusal to license its digital rights management software. Instead, the title of that purchased tune shows up in the display line with a tiny padlock icon next to it; playable music is distinguished with a music note.

But backing out of a song while it played wasn’t as easy as we had hoped — pressing the Back button didn’t do anything. We pressed the Home button, which took us two steps further back than we wanted to navigate.

AM, FM and Internet radio each had its own list of stations. We attached two separate antennas to the SoundBridge so the AM and FM radios could be received, then used seek buttons on the remote and radio itself to find stations. About 100 Internet stations were preloaded on the SoundBridge Radio, but these could be sorted by various categories like name, genre or language.

We listened to various Internet radio stations, including Beatles Radio, Swiss Radio, Smooth Beats, Southern California Public Radio and CNN Radio. But we had trouble with a few stations — like ESPN and Pacifica Radio — that failed to stream content to our radio after five tries. Roku said that this might have been because the stations’ servers were busy.

Without the remote, the Roku SoundBridge Radio functions — but not completely. The six numbered preset buttons are categorized into A, B and C, so there are really 18 places to save a station from AM, FM or Internet radio. You can also use the preset buttons to save specific playlists, as well as lists of search results, by holding down a preset while listening to a song or station in that category. For example, while listening to music from Walt’s iMac, we held down the number six button, and a new label was placed on that button, smartly titled “All songs on Walt’s iMac.”

If the Radio is in standby mode, the time, or the time and full date, can be displayed. Pressing any of the preset buttons will turn on the device and start playing music saved under that preset. Another button brings the Source menu to the screen, but Roku didn’t think to add a select button to the Radio, so we couldn’t navigate far enough to listen to music from the Katie’s Music or Walt’s iMac libraries.

Overall, the Roku SoundBridge Radio is a smart device that needs a little tweaking. If the company really wants to market it as an alarm, it has to understand that users will want to play all of its available music, including computer libraries, without a remote. And navigating with the remote itself needs to be improved so that users don’t feel like they can’t back up out of a menu.

But by designing this receiver with built-in speakers, Roku made it less confusing for average users — a move that might encourage more people to step away from their computers, while still enjoying great music.

• Email: MossbergSolution@wsj.com