If you're using one of the iDevices than it is because it is read as a camera and not a music device. Is it possible for you to stream your media to your xbox?
it used to be possible with a free media update xbox had twice...but apple undid that update with an update to their systems and now xbox cant read the ipod
if you get a 2nd gen ipod or 1st gen with out updates it might still work from the research ive done