To save some cash, get a 6800 (NOT GS or GT) and use the free program RivaTuner to unlock the hidden shaders. It's really simple to do; a Google search will dump a couple hundred tutorials on it, and if not you can email me. As long as you don't mess with the other settings in RT, it won't burn your card either.

Basically, the 6800, 6800GS, and 6800GT are all the same card. nVidia just locked parts of the card off, moreso on the 6800. This way they could mass produce all of the chips and simply lock a couple. By unlocking the pixel and vertex shaders that are blocked off, you take a 6800 and turn it into a 6800GT. I did it and my FR hasn't improved at all, but it's much more stable (as in I can fly into a furball with a GV war under it and see a drop of 10 FR instead of 20).
Just to give a comparison, this computer runs full sliders, 4X AA, at 40-60 FPS (60 Hz monitor)...except on Karelia

-3.0GHz Northwood P4
-Gigabyte GA-8IPE1000 Pro-G motherboard
-Corsair ValueSelect 512MBx2 (1GB), CAS Latency 2.5, DDR400 (PC3200)
-XFX nVidia 6800 (unlocked to 6800GT)
-Sound Blaster Audigy 2 ZS
Nothing's ever been overclocked, unless you count the unlocking as OCing...