XBMC Media Center, a free and open source cross-platform media center software, capable of playing back almost all known video, audio and picture formats.
Installation instructions from XBMC wiki
Start by running this command:
sudo add-apt-repository ppa:team-xbmc
Now click on System->Administration->Synaptic Package Manager->Settings->Repositories->Other Software.
Select the first ppa for team-xbmc, then click on "Edit..."
Change the Distribution to "lucid". Click OK.
Select the 2nd ppa for team-xbmc, and make the same the same change to "lucid".
Reload the packages, and then install "xbmc" as well as "xbmc-standalone". If you want to use the command-line instead of Synaptic Package Manager to do this, here are the relevant commands:
sudo apt-get update
sudo apt-get install xbmc xbmc-standalone
You should now have XBMC in Applications->Sound & Video->XBMC Media Center.
Source from here