Well, what about your CPU:RAM ratio? It's pretty far from 1:1. You could strive to get a 1:1 ratioo, I bet that would improve things. Other than that, I really dont see any other way to get more performance out of your machine without going with better cooling and getting a high OC. But you only have a northwood, so you arent going to see the highest OC on that. Beyond upgrading, or Ocing higher, thats it I think.
EDIT: Why is your AGP only 4x? Getting the proper components to make that 8x will greatly improve your FPS.