1.backup your original VGA bios,of course you can use NVflash
2.download the same kind(make sure there are of the same chipest)VGA card driver and their bios
3.download vgabios from http://file3.mydrivers.com/files/tools/display/nv.zip
4.edit autoexec.bat,add such command line
c:\vgabios\vgabios -f c:\vgabios\xxx.rom
5.make sure there are no mistake and restart your computer