P,S. I've got a funny feeling that the old 3D Mark '01 doesn't really test the card in 3D mode....?
Maybe only 3D Mark '05 does that successfully with the latest cards, and Direct X 9c...?
3dmark01 does run in 3d mode, but only 3dmark05 will truly so you the abilties of a 6600gt.
3dmark01, except for one short badly implemented game test, does not support shaders which are everywhere in modern games. Cards like 6600 gt have vertex and pixel shaders processes that go unused in a dx7 benchmark and are barely pushed in the dx8.1 nature test.
A dx7 card would die if its GPU was told to run shaders (if it could support shaders).
My advice is to use 3dmark05. That benchmark is a true test of your card.