q6600 is great processor, I have mine OCd to 3.2GHz on air cooling
But, I would build my own PC, it really is quite easy, just screw in some pieces, and plug some plugs where they fit, pretty much it only fits one way, and if you don't overdo the force, and if it doesn't feel right try the other way, and RTFM, it is really easy
Sorry, just read you don't know what quad core is 
Yeah, basically quad core allows smart programs to use your one CPU as four CPUs, a core is pretty much a CPU, but it is integrated into one package with others.
This means that instead of having one 2.4GHz cpu you pretty much have four, so four things can be done at once, making a huge difference!