ECS K7s5a lock ups

I just have to begin by thanking you all for your answers to other people's questions. I have read the forum for months and everytime I have a question it's already answered, so this is my first post about a problem I've had with several compters. When playing games (particularly Unreal and UT) my computer will occasionally lock up (picture freezes, not accepting input). Usually this starts with the games and then it will start to happen in other progs (Word etc.). It begins randomly and then becomes a problem. Does anybody have any idea what may be the cause of this. I have experienced this on a PII 350, with 16mb Creative Banshee (retail machine not sure about othe specs), my friends Compaq K7 550 (not sure about graphic card, but believe it's a 32mb Voodoo 4) and my newly self buildt system:

ECS K7S5A Mobo
Athlon 1.4Ghz with Dragon Orb 3 HSF
256 DDR Ram
PowerColor GeForce2 Pro 64mb
WD 40GB 7200 HD

No OCing happening

Running both w2k and 98 SE (I am sorry, but can't remember if this happened under both OS's as it has only happened a few times, but as it has tended to get worse on the other computers I figured I'd ask before it happened again)

P.S. Is the Bios temperature reports correct? It reports 41º for the processor and around 50º on the other reports.

Legalize lutefisk (UFF DA).