I don't think you will be able to do this. AFAIK, you have to use a driver package that is good for all cards that you have in the computer.
After doing a quick check on nvidia.com, I noticed that the GT2x0 Series uses a different driver package than the Forceware. Given that, my believe is that you will be able to run up to a 9 series card, but not a GT2x0 card.
Does a 9800GX2 works for you? Should be the top of the line before the GT2x0 series.