I want to know what my motherboard is without having to open the CPU. I am planning to buy a new video card and I need to find out if my motherboard supports my new video card. The new video card I am about to get is Nvidia GeForce 8800 GT.

I've never used one so I can't recommend a specific tool (easier to pop a couple screws and read the motherboard model directly, truly).

Just Google search for "motherboard detector" or "motherboard detection tool" and you'll find a free one you can try.