In the iTunes preferences you can chose what format iTunes converts to. While AAC is technically a slightly superior codec, as you've discovered, it doesn't play well with most things non-Apple.

For about the same reason as you (and I have been ripping albums LONG before AAC came out) I set iTunes to a 256kbps MP3 format, and have no problems sharing.

I know this doesn't help immediately, but it'll save you time later on..

[This message has been edited by Diki (edited 03-16-2009).]