You can overclock to improve performance on any game, really. Your graphics card and CPU are a little old for new games, though. I'm sure that if you have an Athlon X2, you might be able to upgrade to a triple or quad core Phenom processor. You may also want to upgrade your graphics to a newer GeForce card because the 8400 GS isn't really meant for gaming.
If upgrading isn't possible, though, overclocking might help. I'm not sure that the GeForce 8400 GS would be a great graphics card to overclock, but overclocking your CPU/memory might be beneficial. Remember, though, that overclocking does generate excess heat. If your parts are old, excess heat and strain might not be very good for them.
EDIT: I just looked around a bit, and your motherboard should be able to support a Phenom X3 or X4 CPU. You might want to double check yourself, though. Maybe you can look where you bought the motherboard.
