Vista home pre. crashing in games

i recently got my buddys computer to try and fix a problem with the bsod. although i have never seen it bsod, it crashes sometimes, mostly when playing games such as starcraft 2 after about 20 minutes.

when it crashes the screen sort of bricks the image, as in the screen is usually black or blue blurred with other small lines of black and white.

i have updated the videocard and tried installing windows updates but some of the updates would fail. i have got all but 4 to work. the main one i think may be an issue is the -.net framework 3.5 sp1 family update-.

-does this make any sense?

Yes, As its a 20 minute thing, run hwmonitor from cpuid.org and see what the temperature is.. Sounds like a overheating and artifacting, then crashing.
CPUID - System & hardware benchmark, monitoring, reporting

Now depending on the card, uses evga precision for nvida cards, or ATItool for ati cards and ramp the fan up to max, and see if it helps.

The .net might be another issue.