go to the forums @ evga.com. You will find alot of info on this. Also MVK.net has a program called Nibitor that will allow you to modifyn your vga bios to detect the temps.
What you will need from mvk.net:
Nibitor
the proper bios for your card
nvflash version 5.13
download the above items, and do the following:
1:create a bootable floppy, and put nvflash on it
2:Install and open up nibitor, go to file open, and locate the bios you downloaded.
3:look through the tabs in nibitor until you find the tab that says "6600 temp trick" check it. Go to file and save the bios TO THE FLOPPY you created earlier.
4:Leave the floppy in the floppy drive (duh)

and restart.
5:at the a prompt, type "nvflash -b old bios" (without the " symbols) (this will save your old bios)
6:now, type nvflash (enter the name of the bios you wish to flash here, it should end in .rom)
7:you should now be finished
: