|Now wait a second.|
There is a bug in most of the Nvidia drivers that disables the Video card's fan on some cards. Are you 110% sure that the fan on the card is spinning? Have you visually checked to make sure?
Download Ntune from Nvidia to enable the overclocking sub-section in their drivers and make sure the fan is on and set to 100%.
PowerMac 9600(1 ghz G4)
ATi 9200 PCI