Shoutbox

It's only 5 PCs at one time, you can de-authorize a PC and authorize another.

If you want to buy music without restrictions on it, you need to buy DRM-free music.

I believe you can buy DRM-free music from iTunes, but it costs an extra 30 cents per track.(and whether they actually allow you to do what you want with it I'm uncertain, they may still bind you to a iTunes related machine)