How to play video dvd in Ubnutu 10.04 Lucid Lynx

Install the libdvdcss library.

# sudo su -
# apt-get install  libdvdcss2
# apt-get install libdvdread4
# cd /usr/share/doc/libdvdread4/
# ./install-css.sh

If it says that the package is not found then try them again after executing the below lines:
add medibuntu repositories in your sources list

$ 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 

$ sudo apt-get --yes --quiet --allow-unauthenticated install medibuntu-keyring
$ sudo apt-get --quiet update

Enjoy!