Ok, 9.3 didn't work, but based on the things you've been telling me and the fact that a Vista driver should theoretically work, I figured if I go back far enough it should start working.
To make a long story short, I tried Catalyst 8.12 and, as if by magic, it's working perfectly.
Thanks a whole bunch, I could never have done it without your help.
Edit: Well, it's running pretty slowly, but at least it's definitely an improvement. Maybe I'll mess around with it later to get it running better once I have things set up.