Boosting up the speed of your computer with a new central processing unit (CPU) is an excellent way to do it yourself computer upgrade whilst cutting out the middle man, effectivly saving money.

Checking Compatibility
The first thing you will need to do before looking at CPU's in what your computer is compatibly with. Firstly you'll need to find out the motherboards socket number, this is the amount of pins found on the CPU. Intel Pentium 4 Processors range from 478 to 775 pins. AMD processors range from 754 to 940 on the Athlon 64, Athlon 64 Fx, Opteron and Sempron models. To check the compatibility of the CPU with your current computer, refer to the motherboards documentation to find the CPU socket

AMD or Intel
Comparing Intel and AMD CPU's is like comparing apples and oranges. They both have their strong areas. Intels are generally faster in their information relay, but are more expensive, generate more heat. AMD CPU's are faster in the respect of their base frquency, they are cheaper then their Intel rivals and output less heat. One aspect in selecting the fastest CPU in realtion to AMD CPU's is that their stock speed is lower then their Intel rivals. AMD CPU's that are 2.0GHz are faster then an Intel 3.0GHz CPU. Without out going indepth of Intel and AMD architecure, AMD CPU's send x2 the amount of data in a single clock, so divide their frequency by 2, in this example the base frequency is 1GHz, on the other hand, intel CPU's send x4 the amount of data per clock, so dividde their frequency by 4, so their base frequency is 0.75GHz.

Selecting Your Speed
The speed of a CPU generally determains what your comptuer is capable of. The following lsit shows what can be done with the respective CPU speed
2.0GHz - Run Windows XP and most of its applications
3.0GHz - Use more CPU hungry applications, typically gaming

Additional Extras
Once selected the right CPU, you may consider other items such as:
CPU Cooling - New CPU's output more heat, more then your current CPU cooling can cater for, to ensure that your new investiment dosen't die, this is a worthy consideration. CPU Cooling ranges from Air Cooling, Water Cooling, and now mainstream Phase Change cooling
RAM - Match up your CPU's speed with memory speed. Increase the computers speed even more with upgrading the existing RAM
Video Card - Increase your computers graphic handling capabilitys with a fast graphics/video card.