Why? I have linux running on a spacewalker in my livingroom. It rocks! I use mplayer and xmms. What else do I need? I share/get files via NFS and Samba.
I can tell you that when it comes to watching video files mplayer kicks windows mediaplayers ass! Takes all the formats and has a much better interface when you sit in your sofa. I have a nice little black IR keyboard acting as my remote. It just rocks!