This is rewrite of a howto that I did for Feisty and it just needed a little touch up for Gutsy.
In a terminal type:
sudo apt-get install gstreamer0.10-plugins-ugly-multiverse gstreamer0.10-plugins-bad-multiverse gstreamer0.10-plugins-bad gstreamer0.10-plugins-ugly gstreamer0.10-ffmpeg libxine1-ffmpeg libdvdread3
In order to play copyrighted DVDs, you need to install the libdvdcss2 package. To do this you need to install the Medibuntu repository. You can find my howto here.
Once you install the Medibuntu repository, in a terminal type:
sudo apt-get install libdvdcss2
edited by pHreaksYcle