>FlyingHorse: In Rivatuner (a software), http://www.guru3d.com
under Directx -> shaders -> pixel shaders -> force 1.4
I kept vertex shaders at 2.0 since the GeforceFX handles them properly.
I also use high quality texture filtering in Rivatuner, and a mip map bias of -1.0, these two combined give (near) perfect quality without using anisotropic filtering, so performance stays up.
And believe me, the few pixel shaders there are in the carrier made the game unplayable. I had to drop settings that I can now keep at maximum. Try it! (though with either your TNT or 6800 it's not really applicable)
Till now, it makes a good difference in Painkiller BOOH and FarCry. I haven't tried anything else.