If cars were computers they would come with gas pedal harnesses that allowed only two positions for the gas pedal, not depressed and 2/3 depressed. The car would either be off, or running at one speed which was set at the factory. Overclocking is like taking off the harness so you can decide how much gas to give the car. This also gives you newfound freedom to wreck the car.
Your computer runs at a certain speed for two reasons - it is able to and it is told to. Overclocking is changing what speed it is told to run at. You then find out what it is able to run at.
A cpu runs at a mhz/ghz rating which is the product of the front side bus speed times a cpu "multiplier". This happens at a certain cpu voltage. By increasing the fsb or mutiplier the cpu is told to run faster. An increase in voltage is sometimes required for this to work.
Increasing the front side bus will also increase the speed of your memory, motherboard, and video card, unless you have an advanced motherboard that allows independant settings for each.
Overclocking starts with a motherboard that allows you to change these settings. Your overclocking limits are hit when your machine freezes or no longer runs with stability. Those freezes will come because a component has reached its limit, the cpu, motherboard, memory, etc. A good cpu cooler and case fans help the components to be stable at these higher speeds. Special cooling helps overclocking but is not required.
Try this search...
http://www.google.com/search?q=What%20is%20overclocking?
The also a search of "overclocking xyz", where xyz is the name of your motherboard.
