You can install the XBMC 11 “Eden” release candidate 2 using the XBMC Unstable PPA. Please note that this version is still under development.
To add the PPA and to install XBMC open a terminal window (press Ctrl+Alt+T) and copy+paste the following lines:
sudo add-apt-repository ppa:team-xbmc/unstable
sudo apt-get update
sudo apt-get install xbmc
When XBMC is installed you can close the terminal window and to start XBMC press the SuperKey and type: xbmc
Read more about XBMC 11 Eden: RC2