Sorry cannot help you, just wanted to add that you are not alone. Mine doesn't charge neither. It never has through USB. Thought this was standard for all iPads because they need lots of juice for their battery. I use the charger. For reference, I have a 64gb 3G+WiFi iPad 2.
I speak for the OP (which can be wrong) but since I have the same issue I assume it syncs with iTunes, otherwise he would have said it doesn't, the only issue is that it is not charged, and it even says so on the iPad (next to the battery icon).