What do I have to look into to learn how to build a computer, primarily for playing games, that has outlets going to a tv(a video game system) and uses interchangeable chips(cartridges, whatever) for software?

A starter kit could be something ike the "XBox 360 Notebook Mod"
http://img362.imageshack.us/img362/694/xbox360lappy1dw0.jpg (http://imageshack.us)