Sadly I'm still using a socket A AMD 2800+ 333Mhz FSB with a barton core. I mostly play older game... with the exception of cod4(The fps are **** in it needless to say, my gfx card is a 7600gs).

I want to try over clocking a bit, my motherboard is a gigabyte and isn't that good, but its not a bad board ether. The maximum FSB is 400mhz and my ram is ddr3200 400mhz... since my CPU runs at 333mhz would it be difficult to overclock it too 400mhz?

How would I go about overclocking this and would i see any real results in CPU power?

333MHz to 400MHz is a pretty minor FSB boost so there should be no problems there. But with such an old CPU even an overclock would yield very little performance gains.

It's time to shell out some money for a new CPU im afraid. Especially if you want to run COD4 at a playable frame rate (you'll probably need a new GFX card as well).