So I just figured out how to set up my external Seagate 250G HD to work flawlessly with my Mac. I tried to plug it into a friend's Window's based computer, but the computer would not allow me to access the drive. it says that the device is working properly, but I can't seem to access the drive. DO I need to reformat it again? What do I do with the current data on the drive, do I need to back it up somewhere else?! thanks!