Dual core computer technology is a pretty new thing for most people, but the truth of the matter is that quad core technology is about to become mainstream. Like dual core technology, which included two processors on the same die, a quad core is essentially two dual core machines pieced together. This means there are two dies with two processors on each one but packaged on the same motherboard in a multi chip mode.
The main makers of quad core PC machines is Intel and AMD. Intel uses the Core 2 chip and has just recently come out with the Core i7 which is based on the new nehalem microarchitecture. Intel specifically made this new chip for the hardcore PC gamer. This chip is made to process information in split seconds to bring a computer user fast frame rates and insanely detailed 3d environments.
The main things that makes any computer fast is it's front side bus speed. The front side bus is like a pipe and the faster the Bus speed, the bigger the pipe. If you have a big pipe you can pump a lot more information through it on each clock cycle. Most dual core processors are very fast, but can't run at their full potential because they have a small pipe or Bus speed. Try and buy a computer with a very fast front side bus so that when the processors think, they can instantly get ALL the information to where it needs to be instead of waiting on the pipe to unclog.