The online music market leader, as you may be aware, is Apple's iTunes Store. It has the largest music library in the world and stocks a vast range of musical styles. An album from the iTunes Store will set you back £7.99, which is in line with online competitors. Its downloads are protected by software called DRM (digital rights management) though, which means you can only play iTunes music on an iPod. So if you change players in the future, you'll have to buy all your music over again. If you're going to use an iPod, then the iTunes Store is your only bet for mainstream music downloads.

Napster is one of the more popular alternatives to iTunes. It offers three options: pay £7.95 for an album that's yours to keep forever, or £9.95 per month for unlimited downloads from its library of 3 million tracks. Sounds good, but if you stop paying every month then you can kiss goodbye to every single song. You don't own any of the music, you're just renting it, and it can't be transferred to an MP3 player.

However, it also offers the Napster to Go service for £14.95 per month, which allows you to put your downloads on to a compatible player, but again, the music will still disappear when you stop paying. The tunes will play on most players that support Microsoft's 'Plays For Sure' DRM, which doesn't include iPods.

If this DRM stuff sounds like a terrible and restrictive idea, you're absolutely right. For this reason, eMusic is the second most popular download site in the UK. It doesn't put DRM on its music, so it'll play on any MP3 player and can be freely burned to CD.

Instead of paying for tracks individually, eMusic offers three monthly subscription plans, priced at £8.99, £11.99 and £14.99 a month for 30, 50 or 75 monthly song downloads respectively. The downside? Although its library tops 2 million songs, there isn't any really mainstream music.

eMusic is populated by indie artists, independent record labels and musicians you won't see on MTV. However, it's a great way to discover some fantastic music and you may be surprised by the bands on there you already know.

You may not expect it, but Tesco's online download store is surprisingly comprehensive and offers albums for £7.99. Like all other music stores except eMusic, everything on Tesco is coated in DRM, although unlike Napster, once you've paid for your downloads they're yours to keep. Again, this works with 'Plays For Sure' players and not iPods.

HMV and Virgin also offer music downloads to keep, although Virgin is more expensive at £8.99 per album. Both are DRM'd and neither will work on iPods.

Until the music industry gets rid of DRM, as music fans and most musicians want, you'll probably be better off buying the MP3 player you like the most, buying your music on CD and ripping it yourself, avoiding the whole DRM question altogether.