Considering the rest of his rig, I wouldn't make the upgrade from an 8800GTS to an 8800GT, it will be a performance increase, but I think the money would be better spent on a new CPU and mobo and RAM. Going from an 8800GTS 320 would be like going from a 9600GT to a 9800GT, not worth it IMO.
You can get a 780G
for cheap, it supports the upcoming 45nm Phenoms as well.
And jump on the 9600
before it goes out of stock, seriously, this is an amazing deal.
4GB of DDR2 1066
is only $50.
I went from a crappy X2 setup to my current rig and used the same RAM.
He has DDR RAM, not DDR2.