Why can't I backup with Time Machine initially over USB, then do it wirelessly? My backup is about 97GB, and that would take unacceptably long over our G network, even if I did it overnight. So, I've done the initial backup via USB, but when I have the Time Machine drive plugged into the USB port of the iMac, it will try to do a new backup via a sparse disk image. The USB backup is its own folder. Any ideas? I would really love to get TM working over wireless again. I did it before with my PowerBook, but that backup was significantly smaller.