Can you give me a better idea of your setup? You seemed to indicate that you wouldn't be wireless anymore. Is that because you plan on putting the box next to your theater?
When trying to stream HD video, there are two general rules
1) Quad core
2) Cat5e or better networking
Some people have been able to stream with dual core or cat5 but if you look through the posts here you'll see a lot of people that can not.
You don't necessarily have to have something that is classified as a "home media server". Here is my setup: http://www.muchgooder.com/mediaserver