Building a new computer

I think it's been ages since I put together a computer. I had a Mac for a while and it served me well. I know I can get a Dell or HP for cheap but I want to do it my way. After futzing around for a long time I finally put in the order for a few components. I've acquired a lot of computer parts and it costs me a lot less than I assumed it would.
But this is no top of the line rig. I'm building a Media Center PC, and it will be used for a few games but nothing like Crysis. I've got a Packard Bell that's barely keeping up with what I throw at it. basically watching a few DVDs, torrents, and iTunes. I love iTunes but it's a real monster on such a old PC.