everyone gots some good info here, just to clarify a bit, you have to check the chipset number of the mother board that you have and the compatible processor speeds its supports, this will tell you what you can upgrade too, if not you have to buy a new motherboard and processor and possibly upgrade the fan in the case, as higher processing spees means more heat, i could be wrong on that point, but i think i remember reading that somewhere, hope this .02 helps, it might just be easier and more cost effective to just buy a new pc off ebay, sony vaio can be had cheap, as ive been looking to add a desktop to the pc collection i have, 2 laptops.
-chris