Warning: Depending on the country you live in this might be a violation of your local laws.
In order to play DVDs on your Ubuntu system you have to do the following:
1. Open a terminal window.
2. Execute the following terminal command to install the necessary packages (approve any prompts):
sudo apt-get install totem-xine libxine1-ffmpeg libdvdread3
3. Execute the following terminal command:
sudo /usr/share/doc/libdvdread3/install-css.sh
Done. Insert a DVD into your drive. Totem will open and the movie will begin playing.