Software programs are available to do this but overclocking anything can and often does shorten it's lifespan. Extreme overclocking can cut the life of the hardware in half.
Just because you "can" do it doesn't mean you have to or need to. You have a nice computer as it is, if we're talking about the system specs in your signature. Crysis Warhead from your other thread has painfully high system requirements for decent performance and if it's the only game you can't run on full detail, it may not be worth putting a new card in just for that if you don't play it regularly. You don't go and spend a small fortune putting a sunroof in the car and then go and live in a cold country where you can't use it, do you?