Can't use two i-pods on the same computer

I recently bought a new Gateway with Windows Vista after my first computer completely died. I hooked up my i-Pod, authorized the new computer but had to back up using my back up CDs. However, all went well.

I thought I would be able to do the same thing when I hooked my Dad's i-Pod up. Instead my songs show up in the library when his i-Pod is hooked up. His songs show up in the music folder that appears directly under devices, with his i-Pod clearly listed as the device.

I tried hooking up his i-Pod under a different account and the same thing happens. I-Tunes won't let me backup his music.

Any clues about how to get out of this mess?