A computer processor, often considered the brains of the machine, has the most significant effect on performance and price. If you want a computer to be able to keep up with technology over the next few years you should invest in a fast processor.
Step1
Think about what you will be doing with your computer for the next 3 years. That is about the timeframe for machines these days.
Step2
If you are just using your machine for casual use, such as word processing, web browsing and the occasional card game, consider an Intel Pentium Dual Core or AMD Sempron processor. If you prefer Macintosh machines, look into an Intel Core 2 Duo.Step3
If you are a middle of the road user, who likes all of the above things but also the occasional heavier game and multimedia use (i.e. pictures and mp3s), an Intel Quad Core would be better. The Quad Core is also great for heavy online multimedia games and heavier multimedia use.Step4
If Macintoshes are your taste and you are a heavier user, the Intel Dual Quad Core processors can take care of all your needs.Step5
If your budget allows it, try and spend as much as you can on the fastest processor. This is because technology evolves at a very fast pace and your machine will be able to keep up after a few years. 
