That depends on what you want it to do.
I don't see an optical drive. Are you doing DVD?
Also you didn't mention a visual output device. Are you going LCD?
You didn't mention how you're going to power it either. That's a big one. There's a lot of options. Be careful and read up on power supplies in that area of the forum. A lot depends on your wallet, but don't forget to figure out how many watts and amps you'll be pulling and make sure your solution is powerful enough. The Athlon processor and a 3.5" HDD pull a lot of power. Add a 5.25" optical drive (CD/RW or DVD) and you're looking at a lot of power and heat. There's a webpage that can help you calculate all those power requirements by just clicking on what devices, but I can't find the link. Anyone wanna throw that out here?