I've been using the software(WD Anywhere Back Up) that came with my 500 GB Western Digital external Hard Drive for a few years. It was connected to a 1st generation single 1.8GB G5 tower. The internal hard drive in the G5 was 160GB with an additional internal 320GB drive I added. I just changed to a Mac Mini with a 320GB internal hard drive and will be picking up an external case for the 320GB drive I had in the G5. I'll need to back up both of these drives. Will I need a much larger external hard drive if I decide to use Time Machine? Can Time Machine back up both the internal(320GB) drive and the external 320GB drive? I was satisfied with the Western Digital back up software I was using on the G5(which was running OS 10.4) but I now have 10.6.8 on the Mini which has Time Machine. Any ideas or help will be appreciated.