Download the BIOS file and put it on a boot disk. Check www.bootdisk.com on how to get a boot disk.
Download nvflash (v4.41) and put it on this disk too.
Reboot your computer with the start diskette and run nvflash -b oldbios.bin to save your old BIOS just in case you might need it at a later time.
Now run nvflash -f newbios.bin Replace newbios.bin with the filename of the downloaded BIOS file.
If you are trying to flash a BIOS for a different card then you will get a security warning that the BIOS does not match your card. If you are absolutely sure that the BIOS is compatible you can use the -p and -u parameters to force flashing. For example nvflash -p -u -f BIOS.bin