Im sure he hasnt got a bottomless pocket mactronix please be a bit more considerate. 640mb 8800gts costs a lot more then the 320mb gts.
Even though 320mb is quite a bit less then 512mb, the physicalm performance difference between the 2 cards will always put the 8800gts 320 out ontop of the 1950xt/xtx.
If your card hasnt got enough memory though simply put it will use your ram as a buffer, so dont worry you'll still get better performance then a 1950xt.
Did you actually read what i posted or just the first sentance and jump on your high horse i actually recomended he get the 320 GTS.