So there is a new update for Airport Extreme base station, 7.3.1. I have heard that you can use an existing drive to wirelessly backup your data with Time Machine. So far, I have verified and repaired the disk. It didn't work, so I plugged it into my computer again and this time I formatted it as Mac OS X (Journaled). I plugged it into the airport, and once again it there was no disk to mount. After fiddling with the Airport Utility and enabling file sharing, I went to mount it, but there was only a folder for the back-up disk. What am I doing wrong? Is there anything else to try to get Time Machine to work with my pre-existing hard drive?