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You may find this article helpful with setting up your devices to sync with your computer:
iTunes 11 for Windows: Set up syncing for iPod, iPhone, or iPad
The information in this article can also help with syncing multiple devices:
How to use multiple iPhone, iPad, or iPod devices with one computer
When you are done syncing one device, be sure to disconnect it before syncing the other:
iTunes for Windows does not support syncing multiple iPod devices at the same time.