I have recently upgraded to iTunes 4 on my Mac and now use Apple's AAC instead of MP3 when importing all my music CDs now. But the problem is that my PC which is networked to my Mac can no longer play my music files because it can't play AAC files (they have the .m4a extension). I donwloaded the latest version (6.3) of quicktime for Windows (I am using 2000) and it can't play the files. Quicktime on my Mac and other Macs can, so it is not a copyright protection problem. Does anyone know any PC players that can read the .m4a AAC files or anyway to get the codec so something like Windows Media Player can play them?