I’m partial to Nvidia, I think their products are better overall in comparison to ATI. I’m using the 8800GTS 640mb.
On another note, that ATI card you’ve selected is far superior to the 7600GT. In fact, the X1950PRO probably matches closer to the 7900GS. From what I remember, the X1950PRO also had better benchmark results than the 7900GS. Therefore, if you want best bang for buck, get the ATI.