Ummm... a guide to overclocking!
OK... first off, theres the FSB. The FSB is called the "external clock"... it controls almost everything on the motherboard. The CPU speed, or "internal speed" is derived by multiplying the multiplier by the FSB.
Because the FSB controls every other speed on the motherboard, its important to have "locks" on the PCI and AGP speeds. these locks prevent unintentional overclocking of PCI cards, AGP cards, and onboard components that run off the PCI bridge. be sure to enable locks based on 33/66 pci/agp, not based on a ratio.
Throughout all overclocking, be sure to keep the voltage in mind. raising the voltage keeps more digital "pressure" on the transistors, enabling higher speeds. unfortunately, higher voltages consume more power, bringing higher temperatures. if you raise the voltage by more than one notch, you should get a better cooler.
Memory speed is also based on FSB. you can usually adjust the ratio of memory to FSB. try to keep the final speed of the memory below the rated speed. you can attempt to raise the speed above rated speed by increasing the voltage of the memory. Its usually safe to raise the voltage to the highest setting (usually its around 2.8V)
Now for overclocking the CPU:
my own algorithm is:
increase fsb by 5-10 until it crashes on boot. bring the FSB down from there until you can boot into windows and run simple applications reliably. You know your OC is stable when you can run an intense application for at least several hours. remember that just because you ran a "CPU Stability test" overnight, your OC might not be perfect. run a 3D app, Half Life 2, or Counter-Strike Source is especially effective at testing an OC.
See above for explanations on voltage. remember to keep an eye on your temperatures. It is best to experiment extensively. I took more than two weeks to perfect my OC, and it runs beautifully. Take your time, and be careful with your temperatures.