I've never put a computer together from scratch before, but I have installed video/sound cards and I have a decent handle on the guts of one. What I'm thinking of doing though, is to build some higher end computers for fun, and maybe even turn a bit of a profit on ebay. Does anyone know what all I would need to get started? And is it possible to get every component I need from ebay, or would there be a better place to look? As I said, I've never even tried doing this before, and it's mostly for fun.

I would like to build something with a quick(er) Athlon processor (like 2+GHz), 1-2 gig of RAM, 256 MB video card, custom case of course....something that gamers would be interested in.