how to setup ubuntu to play an Encrypted DVD

VLC media player for Debian GNU/Linux
Debian stable (lenny)

VLC is available in etch, with a quite old version. Install vlc, mozilla-plugin-vlc, the usual way you do it.
Debian testing (squeeze)

VLC is potentially available in testing. But due to the way testing works, we can't guarantee which version, if any, is currently available. Install vlc, mozilla-plugin-vlc, the usual way you do it.
Debian unstable (sid)

VLC's latest packaged version is always in the official Debian unstable branch. However you should still use our apt-get line if you need libdvdcss:

deb http://download.videolan.org/pub/videolan/debian sid main
deb-src http://download.videolan.org/pub/videolan/debian sid main

For a normal install, do:

# apt-get update
# apt-get install vlc libdvdcss2

Debian oldstable (etch)

A version (0.8.6) is packaged in Etch. However, if you want libdvdcss (DVD decryption) support, you will need to add the following lines to your /etc/apt/sources.list:

deb http://download.videolan.org/pub/videolan/debian sarge main
deb-src http://download.videolan.org/pub/videolan/debian sarge main

For a normal install, do:

# apt-get update
# apt-get install vlc libdvdcss2