2.3+ghz CPU (Preferably a dual core processor or better, go with intel over AMD)
I work in semiconductor and I always tell people that bit of advice. AMD chips are less expensive but it is because of a smaller core. They will perform about 75% the operations per second compared to an equal speed and core count Intel chip. Due to this people over clock their AMD chips to get increased performance.
The down side to over clocking a processor: When a chip is made we have tolerances for various layers. How close the chip is made to those tolerances determines how high of a processor speed you will generate. If in perfect conditions the chips architecture should generate a, say, 3GHz speed. As the manufacturing process is further from perfect tolerances the "approved speed" will degrade hence giving us different speeds out of the same core architecture. If you take that core and push it higher then the approved speed you chance causing a de-lamination of the processor layers leading to failure.
Basically think of driving your car down the interstate and not using the overdrive. Ya you can do it and go just as fast as every one else on the road but you will blow your motor sooner then just about every one else also.