This is where Apple fall down a little, so bear with me here. An ipod won't charge fully via a USB port on the PC without the Extra Power dock adaptor. It will however "Trickle" charge, but it's a damn expensive way of doing it.
Did you buy a mains charger? I know they cost a lot for what they are, but worth it in the long run.
This also applies to Ipads (although the not charging symbol appears, it is trickle charging)
If you would like a specific place for all things Ipad, Ipod and Iphone (Don't leave here or the FE will shoot me:)
Come join us at:
Its free, just like this great site (Creeping to FE)