Same overheating problems with imac g5 white 24inch nvidia 7300 gt. Smcfancontrol stop it to crash and those graphic detail but aplication like chrome with a few windows opens specially videos running cause those graphic detail errors to come back. for years i suppose it was graphic card problems and i was thinking on upgrade to 7600gt, but the cost of it is too high (300$) i Havn't clean the dust also uncheck the thermal paste in 6 years. i hope this help me, if does i will sell this machine a soon as posible.