Engadget has posted a tutorial for streaming media across your home network using previously-mentioned VLC media player.
[W]e are going to show you
how to
stream any type of media file from your computer to another device on your network. We will also demonstrate how to remotely control VLC using any web browser. Using these techniques you could stream video from your office computer to a laptop plugged into the living room TV and control the playlist with your PDA.
The tutorial is detailed and easy-to-follow, so you should have no trouble getting your videos up and streaming in no time.
How-To: Stream almost anything using VLC [Engadget]