I think I have messed up my current vista install about as much as is possible without seeing any blue screens. One of the little annoyances running the beta on a tablet has been that the pen buttons don't work. So I decided to see if using a different keyboard driver for the buttons would help. I expected that only the tablet buttons would be affected, but it disabled the keyboard and touchpad as well. I'd already lost the tablet driver, so now everything works except that there is no working input device, even in safe mode. Guess I won't be able to wait for the next build before reinstalling.