Would an i7 CPU motherboard only support i7 processors? Or can i stick Core 2 Duo In there?

The Intel Core 2 Duo processors are Socket 775. They will of course need a Socket 775 motherboard. I'm sure you will be able to find a high end motherboard with Socket 775. I'm assuming you are going for the E8400 processor? Just a guess! Perhaps the Asus P5Q3 motherboard would work well? Have a look around and see if it will support your system.

It only supports i7 There is no non i7 board that can even come close. My socket 775 board with E6400 took about 45 min to encrypt a movie. The i7 920 does the same thing in less than 15 minutes!

Core i7 motherboards can only support Corei7 Processors and DDR3 RAM. So if you are gonna get i7, you will neeed a whole new motherboard and ram if upgrading from core 2 duo. Core 2 duo and quad core processors are only compatible on core 2 duo and quad core mobos. If you want to stick with core 2 duo and quad core processors, get Nvidia 780i Chipset for mortherboard. Has 3 way SLI, 3 PCI-E slots, and is probably the best mortherboard for quadcore/ core 2 duo.

i7 uses a different architecture for the CPU so, it is unlikely the older CPUs can work on its motherboard.

If, it only says i7, that's all it supports. I actually just looked, and I don't think that this mobo supports anything below i7. Hope I helped