Are the files you're trying to import to your phone from the iTunes store? The phone will not play locked (or protected) AAC files.
I have my music collection on a PC running XP encoded as AAC files from iTunes. My wife just got a KRZR and wants to put music on it. I have read the KRZR can play AAC files, but they are not working for me.
I have not connected a USB cable to the phone yet to sync it with my computer. I used an SD card reader and just copied files over from different folders.