Game Booster, I tried it, do not bother with it. I was not able to discern any gaming help from it.
Vista Services Optimizer is another such piece of software, its free, theres no discernable difference, when I game, with game mode enabled or not. Just an FYI.
Games are about cpu, ram and vid card. OC'ing these components will give you a truly discernable change, but you risk your hardware???????.