First install software you need:

apt-get install mediatomb vlc-nox ffmpeg ffmpegthumbnailer

add this to your config.xml:

<online-content>
[..]
<sopcast enabled="yes" refresh="43200" purge-after="50000" update-at-start="yes"/>
</online>


<transcoding enabled="yes">
<mimetype-profile-mappings>
[..]
<transcode mimetype="video/sopcast-x-ms-wmv" using="video-generic"/>
</mimetype-profile-mappings>
<profiles>
[..]
<profile name="vlcmpeg" enabled="yes" type="external">
<mimetype>video/mpeg</mimetype>
<accept-url>yes</accept-url>
<first-resource>yes</first-resource>
<accept-ogg-theora>yes</accept-ogg-theora>
<agent command="vlc" arguments="-I dummy %in --sout #transcode{venc=ffmpeg,vcodec=mp2v,vb=4096,fps=25,aenc=ffmpeg,acodec=mpga,
ab=192,samplerate=44100,channels=2}:standard{access=file,mux=ps,dst=%out} vlc:quit"/>
<buffer size="14400000" chunk-size="512000" fill-size="120000"/>
</profile>
</profiles>
</transcoding>


Download the Linux Client from Sopcast.com and put it somewhere in your path. Done.

For completeness you can download my config.xml and a additional transcoding script.

Reference: Mediatomb 0.12 on PS3: video thumbnails, YouTube and Apple movie trailers