Installing a server environment for streaming media is really system-type agnostic, meaning it does not matter if it is on a desktop, laptop or netbook.
My suggestion, however, would be to set up the desktop you have hooked up to your TV as the server, though, and install Mythbuntu on it. Wrapping up a complete media centre is "easily" done with MythTV. I quote "easily", because from what I have heard, MythTV is a b*tch to set up.
You can always control it with a laptop/netbook, though.