It's long been an art, but is it actually safe? Steven Xu digs a little deeper...
Since the old Pentium 3 processor arrived, cooling systems of all kinds started being invented. Before you start doing anything to your PC, let's get to know the precise definition of overclocking. "Overclocking is the process of forcing a computer component to run at a higher clock rate (the fundamental rate in cycles per second, measured in hertz, at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another) than designed or designated by the manufacturer".
Now you know the definition of overclocking. You'd better get thinking whether you want to overclock your PC or not. I, from a personal point of view, like overclocking my PCs because I like the feeling of my PCs (mainly Pentium 4's, but a lot of Core 2 Quads) beating high performance PCs in terms of processor speed etc.
If you decide to continue, you must understand that you may have to spend quite a lot buying the cooling systems, as if you are only going to spend money on cheap air cooling, your overclocked PC will "overcook" instead of overclock. If you are going to want to overclock PCs like crazy maniacs like myself, I recommend liquid nitrogen, but water cooling will pass the test. If you were an Eskimo, I believe you wouldn't have any trouble finding cooling! (laffs)
Your PC's hardware may also be a problem, as some are hard to manipulate and some motherboards are just incompatible to overclocking. So your best bet for overclocking is to purchase or build a custom system.
Overall if you have a good cooling system or live in Antarctica, you have nothing to worry about.
