well i am upgradeing my little brothers pc and we got 75 dollars together to get a video card he plays a lot of WOW and americas army it has a pentium D 820 and 2gigs of pny pc2-6400
9600GSO is better than 4670 in most games BUT 9600GSO is more power hungry.
http://www.gameplanet.co.nz/features/132550.20081110.GPU-battle-4670-vs.-9600GSO/page2/
edit: 375W PSU will probably not cut it for 9600GSO.
I'd go for a 4670, those p d require quite a lot of juice.
Also pretty sure the 4670 is on par with the 9600gso, and with aa, high resolutions its beats it, Altho there are a lot of diff 9600gso so i could be wrong