i think when you rip off itunes, you can choose to rip it to the mp4 format. MP4's will only work on apple stuff i think, like ipods, but no your regular generic mp3 players. I have a genric 256mb mp3 player and it wont read the mp4 files.
mp4 or m4a has a better compression scheme than mp3, that is, you get a better sounding audio file that takes up less memory than an mp3. only itunes or ipods play them, but man if you into mp3s and digital music you should have itunes anyway cause its the best mp3 player.
