just to clarify:
in order of price, the cards are:
7600gs- $80
7900gs- $175
x1950pro512mb- $180
and it just so happens that those are all AGP 4x/8x. and it also just so happens that they are listed in order of performance from least to greatest going from top to bottom, x1950 being the best.
the x1950pro is a stunning card. if at all possible go for it. i only suggested the 7900 because it seemed you were sticking to nvidia graphics.
the 7600 can play a lot of games, and it certainly is going to be better. BUT...it's already beginning to show signs of age. the other two cards, though not as old as the 7600, but still being old models, perform admirably. the x1950 pro was proven to play games as tough on graphics as bioshock and still maintained decent graphics and framerates.
if you want the BEST possible bang for your buck, you know what to go for. but i'm warning you now. if you get the 7600, you'll find that there is much to be desired that it just doesn't have. you're going to end up wishing you had waited and bought a different card, or you're going to end up upgrading again in the near future.
i'd say go for broke, and plan ahead.