About a month and a half ago I got a 1 TB external HDD that I have been using as a Time Machine drive. However, two issues have arisen. The first is, I am running out of internal HDD space -- I have less than a gig! The second is, I am interested in upgrading to Snow Leopard. I need more space on my internal HDD, obviously. To accomplish that, I was thinking I could backup school documents, pictures, and video to a separate partition on the HDD. That way, I don't have to restore my computer to a previous backup every time I want to access those files. However, that caused the question to arise, does Time Machine back up simply things that have been changed, who does it make a whole new 'copy' of my HDD each time it backs it up? In other words, will it eat external HDD space 150 gigs at a time, or by, say, a gig at a time? Clearly, I don't have a very good understanding of how Time Machine works. The last question regards my Snow Leopard upgrade. Can I restore my computer to Snow Leopard using a Leopard time machine (assuming the upgrade doesn't work correctly in the setup)? I hope that all makes sense. If not, let me know, and I will attempt to clarify it. Thanks!