Weak system? Really? This computer is not that old, not that it was the latest and greatest when I bought it. And AH doesn't seem to be that graphic intense of a game. I have like 36 processes running but I have no idea which ones I can turn off.
NO! your system isn't weak, DktrEvils system is weak. Your I think has a heat problem, thats way I want you to try the fan idea. If you were locking up after a half hour, the fan might push it to a couple of hours. If it works like that then we have to find out if its your video card, or motherboard thats over heating.
BlackVipers page is a great help in figuring out which to kill and which to leave alone. He list most of the common ones and what to do with them. For those he doesn't mention, google it. The first couple of hits on google usually is enough to let you know if you should kill it, or leave it alone.