what?
Core i7 is on 1366 socket, dual and quad cores on 775 socket. Core i7 is new technology and cheapest build (CPU, mobo, 6 GB tri channel RAM) is about 650 at least. Very decent build with 775 sockets is less expensive and you can get it for 350.
What are you going to do on your PC? …gaming, applications, light/heavy multitasking, programming, photo/video encoding-editing?
Try to by more specific and do not forget to mention your budget…