Theres a good overclocking thread(stickied) at the top of the page
The basics are
1. Lower ram ratio
2. Increase FSB (FSB * cpu multi = ghz clock speed) ie 266x10=2660 or 2.66ghz
3 Test for stability
When the CPU becomes unstable as you increase the speed you can regain stability by increacing the vcore(cpu volts) but this increases heat and power consumption and has a degrading effect on the lifespan of the CPU(but will not likely shorten the USEFULL life of the CPU). You can overcome the additional heat with good aftermarket CPU coolers.