Wii Media Center X is a Java-based web media server that you can have up and running in about 15 minutes. After downloading and unzipping the application, just run the following command (from the mediacenter folder) to start it up:
java -jar MediaCenter.jar
Run this on any machine that your Wii can see and you can use the Internet Channel web browser to access your media center at http://x.x.x.x:8192/.
I’ve noticed a few problems with playing audio files and the video isn’t sized optimally (you can zoom to adjust for this), but this shows a lot of promise. With this running on my primary desktop machine, I can encode/download FLV files that I want to watch and MP3s that I want to listen to. You just drag them to the Video/videos and Music/music folders. You can do this during the day as you come across things, and then you can view and listen to media in your living room whenever you like.
With a little spit and polish, this could be like having all the AppleTV or Windows Media Center functionality right on your game console.