How to overclocked CPU?

I need to overclock my CPU from 700 Mhz up to about 1.2 ghz. Is this possible, keeping in mind that I am capable of attaining a really good liquid cooling system?
If so, please tell me how, to my shame, I know little about hardware, besides what the benchmark numbers mean, and stuff like that.

I wanna play HL2 dammit!

Dude if you can obtain a "really good" liquid cooling system, then get a fucking new computer for that money not overclock some 700mhz junker. Your HL2 probably won't run well on it even if it's overclocked.

And btw it's not plausible to overclock a 700mh that much anyway, cuz you'll run into serious stability issues most likely.