Here's how you can install Cairo Dock 3.2.1 to your Ubuntu 13.04 system.
1. Open a terminal window.
2. Type in the following commands then hit Enter after each.
sudo add-apt-repository ppa:cairo-dock-team/ppa
sudo apt-get update
sudo apt-get install cairo-dock cairo-dock-plug-ins
For more, see the original article at the link below.