There are only three ways that I know of, Asa has mentioned one already..... burn to CDRW in any audio format then 'rip' back in Mp3 to your hard drive....
or you can use software such as TUNEBITE which plays the song and records an unprotected new version for you to do what you want with.....
Tunebite
or as ricky has mentioed, you can use hymn or iopener which allows you to remove the protection from aac/.m4p files which then become .m4A (unprotected).
Hymn and iopener
there is another program called irevolt that removes protection
irevolt
Cheers