Help needed - error code 43 on graphics card

[mycomputerhatesme]

Not sure whats going on... Was playing Oblivion when my computer crashed and since then I can only get 4bit graphics. Had a "host process rundll32 has stopped working" error and my video card (nvidia geforce 8400 gs) had error code 43. I've done system restore and cleaned out some problem programs and rundll32 error has not come up but cant get rid of error 43.
I tried updating driver but didn't work so tried to uninstall then reinstall now it says "windows found driver software but encountered an error while attempting to install it - the system cannot find the file specified"
I've been advised to try a registry repair program but I've also been told they can do more harm then good...
Would reinstalling vista itself help? I've never done that before and I'm scared I'll loose some of my files. I've backed-up but working in 4bit graphics means I can't see if I've selected or de-selected options so not sure if I've gotten everything.
I've had this system for approx 18mths and never had a single prob until now, does anyone have any suggestions?
I'm using vista, my system is a quad core with 2gb ram. I'm not completely computer illiterate but I'm not too knowledgable either so if anyone can help it would be extremely appreciated.