Itunes prefers aac files, but you may need an additional linux package to support this: http://linuxappfinder.com/package/gtkpod-aac
On your profile, note down what distro you are using, it helps us to help you- if ubuntu, you can open terminal and
sudo apt-get install gtkpod-aac
Welcome to linux! Everyone started somewhere, you just have to keep hacking, keep asking, and keep backing up...