I plan on building a kick-ass gaming pc this summer, but i'd like it to be able to boot OS X also.
I assume I can use any HDD, Memory, DVD-RW but that I will need certain CPU and Motherboard.

What chipset should I get?

And is my options of Graphics cards limited or do all new graphics cards have drivers for OS X?
Will I be able to just install OS X from my Leopard Disk that I bought from Apple?