Your first option is to download a program capable of converting AAC/MP4 files to MP3, WAV, or WMA files. For this I recommend the program Easy CD-DA Extractor, which has a 30-day free trial. It will get the job done provided the music is not copy protected.
Your second option is to have him dig out all of his CDs again and use a program other than iTunes to rip the CDs. Windows Media Player, for instance, has the ability to rip to MP3, WMA, and WMA w/DRM. (I believe the default setting is WMA w/DRM, so he'll want to change that before proceeding.) A good free alternative is Audiograbber, in case you don't like WMP.
Hope this helps,
John
my nephew has used itunes to rip all of his music to his computer and for christmas got a zen neon, which wont play the mpeg4 files which itunes has ripped all his music to.
None of these files were bought from apple so nothing illegal needs to be done rather we only need to convert these mpeg4 files to most likely mp3's which everything plays.
Again i dont need to crack or get around any DRM as they arent bought off itunes just ripped with itunes....

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic