After much searching through my files, I found the name of the BIOS modder that I used to use:
Ray Adams' program, RVBEdit
The program itself should be in English. If not, I've got a version that is.
At the bottom of the page are links for nvflash and DOS4GW.
I don't really remember much more about usage of them, as it's been years since I had a Geforce2 card. I know that it's similar to a motherboard BIOS flash, except for that DOS4GW program.