There is precious little in the way of written documentation about the following, but iTunes 7.1 is now reasonably accessible under VoiceOver on Mac. (There are a couple of sources, but very little in the way of actual user testimonial on the MacVisionaries list [example].)
The best way to learn about it is to listen to Episode 10 of the Screenless Switchers podcast (also subscribable at iT(M)S), where our hosts pretty much do a tutorial of how to use iTunes under VoiceOver. A few small things are still impossible, and a lot of things seem inconvenient, and there hasn’t been enough work done on how to read data on the iTunes Store properly (“3:00” alongside a song title means “three minutes,” not “three o’clock”), but for a V1.0 product, things are coming along well.
(And on the other hand, VoiceOver pronounces “Gnarls Barkley” perfectly.)
To my knowledge, Windows screen readers can barely do anything with iTunes. And iPods are hopeless save for the iPod for Losers™, the Shufflé. (Curiously, there seems to be an entire list on the subject, Blind iPod.)