talk of overheating, yes, i ran into those just last week.
a student of mine had a prob with his system & that most apps, especially 3D games couldn't run.
turned out that his geforce 4 mx440 card (the el cheapo version) had only passive cooling(plain heatsink with no fan).
my suggestion is that if u do have an old processor(like amd k5, pentium mmx) lying about, take its fan & screw it into your graphics card heatsink.
be careful & don't bend your card too much when screwing in the fan.
if u don't have a small fan like that, then time to go to your nearest computer shop & ask if they have any. or maybe u should ask your friends or cousins or ...
hope that helps though not much.