Radenight & Montyuk - Thanks for the replies.
I can boot to safe mode, no problem, but I guess I should have checked the device manager while I was there (d'oh!). I'll check it later when I get home later tonight.
My graphics card is a gigabyte ati HD4670, and its connected to my LCD via DVI. I'll try switching to VGA and see if that works. Could be the driver since I have a few problems with the graphics driver even in vista.
I installed Windows 7 on a separate HD from vista.
I forgot to mention something else which, hopefully, could give a clue as to what the problem is - When I press CTRL-ALT-DEL, my screen goes blank. The desktop comes back when I press ESC. I guess it could be a graphics driver issue. Any recommendations on which driver I should use?