See How to play DVD Movies in Your Ubuntu Box
Ubuntu 9.04, 9.10, 10.04 (i386, amd64) and 10.10
Install the libdvdread4 package (no need to add third party repositories) via Synaptic or command line:$ sudo apt-get install libdvdread4
Run the following command
$ sudo /usr/share/doc/libdvdread4/install-css.sh
Another Way
Add mediubuntu repositories$ sudo wget --output-document=/etc/apt/sources.list.d/medibuntu.list
http://www.medibuntu.org/sources.list.d/$(lsb_release -cs).list
$ sudo apt-get --quiet update
Update Key
$ sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring $ sudo apt-get --quiet update
Install the following packages
$ sudo apt-get install libdvdcss2
$ sudo apt-get install libdvdread4
$ sudo cd /usr/share/doc/libdvdread4/install-css.sh