For first time users, here are steps to help you guide through the installation.
Bring up the terminal (Applications -> Accessories -> Terminal)
Edit the /etc/apt/sources.list by issuing the command sudo gedit /etc/apt/sources.lists
Scroll down to the end of the page and paste the following lines:
deb http://ppa.launchpad.net/qgis/ubuntu jaunty main
deb-src http://ppa.launchpad.net/qgis/ubuntu jaunty main
Saving and closing the file, brings back the prompt.
Update the package lists using the command, sudo apt-get update
Install Quantum GIS with sudo apt-get install qgis
Ignore any GPG errors that show up for public keys that are not available.
Access Quantum GIS from Applications -> Education -> Quantum GIS



