I currently have a iPod nano 8GB. but I have 2 different libraries, 1 on my windows desktop, and 1 on my macbook. both altogether are 10GB, (4GB for windows, 6GB for Macbook) the whold 4GB windows library is in my iPod Nano, and I just want to pick some songs from the macbook library to add to my iPod. How do I do this without completelely wiping out either one of them? Every time I hook it up it asks me if I want to sync the iPod, which will erase all my songs in the library.