I also have a Socket 754 clawhammer 3700+. I bought a PCI Express motherboard on newegg, and put a 7600 GTS in my system, and got another gig of ram. I am very happy with the performance I got when I jumped from the 5900xt, and 512 MB setup to this new setup.
Most games I play in 1024x768 with 4x AA and 16x AF. I do get quite a bit of lag in City of Villains but I think that's just the game itself. I may even buy me a 8800 640 MB and a new monitor towards sometime this summer, and upgrade my CPU, etc some other time.
Look into the EpoX Socket 754 board on newegg that has SLI. I have the Albatron board that was out for a while. I paid only $25.00 for it after mail in rebates. Boy, am I glad I bought it.
Game Ive played with no lag with this rig
Quake 2 * of course* 4x AA 16x AF
Q3 Urban Terror *of course* 4x AA 16x AF
CSS in 1024x768 4x AA 16x AF
BF2 in 1024x768 4x AA 16x AF
Doom 3 1024x768 4x AA 16x AF
F.E.A.R 1024x768 4x AA 16x AF
SilkRoad Online 1024x768 4x AA 16x AF
WoW 1024x768 4x AA 16x AF