First off, there is a lot to know about overclocking...
Make sure that you know what your getting into. Doing something slightly wrong when you attempt to overclock can lead to destroying your processor and motherboard. Also, if you are going to be overclocking know that if you mess up anything your manufacture is going to help because you'll be voiding all warranties and stuff. Next, make sure that you have a good, no wait, great cooling system installed in your case because when you overclock you are going to be going at some serious temperatures. Since your computer is probably already running at 100 + temperatures at normal speeds, if you overclock its going to be getting past 150. If you don't want to fry your processor I would recommend buying a great cooling system. If you don't want to spend money or you don't have any you can just take the side of the case right off and use a floor fan. If you know you want to overclock please note that you are going to be tinkering with the BIOS and that is potentially dangerous as well. What you have to do is set the front bus speed and multiplier higher inside your BIOS. The front bus speed is what your computer runs at and then multiplier is what makes it run faster. So like for instance if you have a 100mhz fbs and a multiplier of 12x then its going to be a 1200mhz computer. For overclocking what you have to do is set these two higher so that the speed runs faster than normal. You may not be able to overclock because some of the newer companies are making it so you can't access and change the multiplier (This is why I can't overclock).
If all goes well I would expect that you could get up to 3ghz or possibly less. I don't want to sound mean or anything when I mention all these warnings but unless you really need the speed, I wouldn't overclock.
