If you're running XP it's in administrative tools in control panel. I'd recommend turning off the reboot on error option, and the reporting is on by default so you shouldn't need to turn it on (look for the event viewer in administrative tools). While you're in there, you might want to turn off system restore and reboot on error, see if that takes care of anything. It is hard to tell the difference between GPU errors and CPU errors, they both have similar effect. I don't know about AMD, but with Intel it's really difficult to get an RMA for a CPU. I know on a similar thread on another board, they basically wanted you to try another CPU to see if it fixed the problem before giving RMAs.
The things you want to check are memory (memtest extended tests), Prime95 (won't tell you if the CPU is bad per se, just if you're stable at a given clock), see if you have problems with 3dMark03, and a minimum install (remove all of the cards and install, then install back 1 at a time to see what's causing the problem). I'd say, given the information you've provided, that the CPU is the culprit although memory, file corruption, bad components (card), video, and PSU can also cause random restarts.