CPU lockups are one of the most difficult problems to trouble shoot.
You might have a software or hardware conflict (usually the culprit. loaded any new software lately?), your memory chip might suck, your processor-mobo-or hard drive even could be overheating (do you have a case fan in addition to CPU fan?), your disk drive might be fragged (try defragging), are you good on disk space? (you should be with a 40g), last but not least...when was the last time you restarted your machine? I can usually go for 3-4 days without restarting if I'm not hammering the machine. After that the system resources start dropping too low and performance starts to suck.
I'm running Win98, 450 k6-2, 256ram, 8g hard drive so I have to be on top of all those above things to keep the box running right. Plus I have all kind of peripherals attached so that saps resources too.
