Do you know what model your motherboard is? Some motherboards actually cater to overclockers by allowing them to change frequencies and clock ratios via the BIOS setup program.
Other motherboards use a series of dip switches or in some cases jumpers to manually set processor speed. Basically you have to know your motherboard in any case.
Another thing to consider is you should overclock gradually. Just clicking your proc from 1.6 to 2.0 GHz will be pretty detrimental to its health. Personally I would suggest going up in 50MHz increments (some may even consider this too high) and then let the machine run for a day or two just to make sure it's stable, handling the speed ok, and not overheating. Then if it's ok go up another step. In some cases you may also have to increase the voltage being delivered to the CPU a little bit, which can be fairly dangerous.
Just keep in mind any attempts at overlocking voids any and all warranty.
Not to mention the fact that a new processor is cheaper then replacing a fried motherboard/processor combo and possible other hardware.
Threaded Mode