I agree with in_core. Even if you switch to the GTX470 or 480... you will not notice much difference from your current system. Wait for the sandybridge setup and upgrade all if you can... Because your framerate will only increase slightly with a new CPU or graphics card in your current setup.
Hell, my last system was an ASRock P43D1600Twins with Core 2 E7500 2.93GHz, 4GB DDR2 800, and NVidia 9800GTX 512MB and it could still play Bad Company 2, Modern Warefare 2, FarCry 2, Left 4 Dead and Batman just fine with mid to high settings... and what you got is a little better than that.
My new system is AMD Phenom II X4 965 BE 3.4GHz Quadcore, 8 GB DDR3 1333, and NVidia GTX465... And I can play all the same games on the ultra high setting... I am just waiting for the i7-2600 sandybridge systems now... so I can run SLI with 2 480's
hopefully!