The easiest way to start out is to disable what saint19 suggested - Cool'n'Quite, C1E support and PCI-E spread spectrum.
Then raise the cpu multiplier one step at a time and run a stability test (eg prime95) for 30 minutes at least. When you get to a point where the stability test fails, increase the voltage minimally and repeat the stability tests.
Where you stop is when your temps reach too high, at which point you need a better cpu cooler to further the oc. I'd stay as far below 60C as i could. my pII x4 955 i kept at 3.7Ghz running at a cool <50C at 100% load