I have to agree with lance. Save your money now. Buy yourself an ok graphics card like a 7900GS or x1950PRO, and use the money you saved to certainly get yourself an X2 and maybe do a RAM upgrade.
Besides, if you dump $600 you could have spent on the above parts into a 8800GTX, everything else in your pc will bottleneck it for sure. Take care of your other hardware first, hold yourself off with one more dx9 card, and wait for ATI's r600 so you will KNOW you made the right choice instead of only guessing you did.