Use nbittor from www.mvktech.net. It's under the nvidia download utilities. Back up your bios using nvflash, Open your bios from the floppy via nbittorr and make a new bios & save it to the floppy. Nbittorr will allow you to change your fan speed and enable the temperature sensor hack for the 6600 just by adding a check in a box. Flash the new bios which is mostly the same bios you have with the modification. I'm honestly not sure if it will work for the 6200 card though. Your doing this at your own risk btw I have a feeling that it might work out for you.
quite easy actually. I have NEVER had one go wrong on me, I have however heard of some horror stories. Anyway if your in doubt then I suggest you dont try it. Best to follow your gut