Well it went through an entire install without locking up. I never even considered it but Evelmunky seems to have been right. I disabled the cd drive I was using and used the other one I had and it didn't lock up. I'm going to partition the HD and install XP 64 and maybe the new Vista build to try it out. If it takes both installs and doesn't lock I feel fairly conifdent that that was the problem the whole time.
I never would have thought about the CD drive but looking back it does make sense. Everything in the computer had been replaced with known working parts except the MB, CPU and CD drives. Can't say for sure that's the problem yet, could have just been lucky. I had almost made it through installs before so I really want to test it and see if that was the problem.
Hmmm one question though. If my drive was bad would that really cause severe sluggishness of the OS with regular use? In other words, just being connected but not being used, could it cause the entire OS to slow to a crawl? That may have been a seperate issue I didn't know about but solved while changing other parts (memory for example or adding new thermal compound).
I'll let you know if it takes the other installs without any problems and thank you everyone for your help. It helped me know what other things to look at if problmes arise.