if you rip cd's to wmp, they will be wma format. don't know if you can change rip settings on wmp to allow say mp3.
if i rip cd's to realplayer as mp3, then import to wmp, it stays as mp3.
realplayer you can set to rip as mp3 or m4a for instance.
i-tunes auto converts wma's to mpeg audio or aac audio to allow for i-pod.