XBMC is an award-winning free and open source (GPL) software media player and entertainment hub for digital media. XBMC is available for Linux, OSX, Windows, and the original Xbox.
Currently XBMC can be used to play almost all popular audio and video formats around. It was designed for network playback, so you can stream your multimedia from anywhere in the house or directly from the internet using practically any protocol available.

How to Install XBMC MediaPlayer in Ubuntu 10.04

sudo add-apt-repository ppa:team-xbmc/ppa
sudo apt-get update
sudo apt-get install xbmc-standalone