I just got a MacBook Pro recently and am looking to have it backed up via Time Machine. I already have an iMac and a 500GB External HD that I am using to back that up. I think 500GB would be plenty to back up both machines, but I don't have any idea how to have both of the computers using the drive at the same time. My first idea was to do it over my wireless network, but for some reason the wireless in this particular room is not very reliable and so it does not seem to work very well. My most recent idea was to have them both connected via USB, but I would imagine I would need a double male splitter and I'm not sure if they exist, or are reliable if they do. Any help would be greatly appreciated.