Do you mean a quad core processor mate?
I'm a little sketchy on exactly how it tots up, but my own laptop is 2.53ghz dual core, and I can play games which requires say a 3ghz single core processor.
I don't think it is as simple as saying 2 x 2.53 = 5.06 ghz processor (in my case) but it certainly does boost you past the single core capability or I'd not be able to play a good few games which I can do.
Normally, the benefit of multiple cores is that the program can assign different tasks to run on different cores simultaneously, so instead of processes queuing up to all run on the same core, they can run on two cores, or four etc so the application can work faster/more efficiently. It does depend on the program tho, and some are not written to support multi-core precesors, tho the majority of newer programs will at least support dual core, if not quad.