The GeForce 8800 GTS 320 has 96 CUDA Cores compared to the 64 on the GeForce 9600GT, giving the 8800 a significant stream processor advantage. This allows for less of a bottleneck within the card.
The GeForce 9600 and the 8800 are just as fast as one another, having a graphics speed of 650 MHz and a processor speed of 1,625 MHZ.
The GeForce 9600GT has 512 MBs of internal GDDR3 RAM, while the GeForce 8800 GTS 320 has only 320 MBs of internal RAM. This gives the 9600 a distinct advantage.
Both cards are completely SLI compatible, using the exact same Nvidia technology.
The 9600GT is much cheaper than the 8800, being found new for around $80 to $120, while the 8800 averages around $250 new as of July 2010.