Dual Core is exactly what it says on the tin - 2 processors, only they're linked so they work together. It doesn't mean you get quite the performance of 2 processors though, only about 80% extra compared to a single core.
When I build my machine I'm also going to link up 2 graphics cards through SLI
If you get someone to build your pc or do it yourself you can get that spec much cheaper than £2k, and if not go to MESH for good deals on brand new machines.