The 7900GT supports Inverse Telecine and Bad Edit Correction. The GeForce 7900 GS does not. Overall the 7900GS will deliver performance a little below that of the GeForce 7900 GT. The 7900GS features lower power consumption and is based on a 90nm chip process.
One of the main differences between the GeForce 7900GT and the 7900GS, according to NVIDIA roadmaps, is that a single quad has been disabled (bringing the total number of pixels per clock to 20) and the graphics core and memory are clocked lower.
Its a great card of you want something that is economically priced and performs between the 7600GT and the 7900GT Graphic Cards.