I would like to build a small home game server specifically to run Source. I have a Dell Dimension 9150 (specs) that I'd like to use to salvage parts from (I'm thinking the Pentium D and the HDD('s)). I also have $200 for additional parts. The reason why I'm not just using the Dell is because it's huge and cumbersome and I'd like the server to be as small as possible.
This the build I tried to put together but I'd greatly appreciate some suggestions: