Tady je postup, mnou nekolikrat overeny na TNT2,GF1,GF2MX,GF2PRO,...
NVidia changed the options in version 3.00 so here is a tutorial on how to flash your BIOS using NVFlash 3


First of all... Backup your BIOS!
Download NVFlash 3.03 (or newer), (in the BIOS -> Flashing (& Dumping) Tools area) and DOS4GW (also in the BIOS -> Flashing (& Dumping) Tools area).
Extract all files in one directory and copy the reference bios you wish to flash also in the directory.
Restart in MS-DOS mode (Press F8 while booting, choose Boot to MS-DOS Prompt).

Go the directory where you had extracted everything and type: "NVFlash -r". This will disable write-protection in case it is activated on your card. Your monitor might turn off for a while but that's ok.
Now type: "nvflash -fBIOSNAME.ROM" (Exchange BIOSNAME.ROM for the name of your bios. Example: "nvflash -fnv5bt.rom"). Your monitor will go in a stand-by (up to a minute). DO NOT RESTART THE COMPUTER UNTIL THE SCREEN HAS COME BACK!
Now relax and press CTRL-ALT-DEL. If everything had gone right than your system should now display the newly flashed BIOS. If your system doesn't come up you fucked-up your card...