Using Command Line (Only for advanced Users)

To enable the universe and multiverse repositories using the command line, you can execute the following steps:

Open a terminal and open your sources.list file using the following command

sudo gedit /etc/apt/sources.list

Assuming you are using the default sources.list, you should be able to replace everything currently in that file with the following

## MAIN REPOSITORIES
deb http://gb.archive.ubuntu.com/ubuntu/ hardy main restricted universe multiverse

## MAJOR BUG FIX UPDATES produced after the final release
deb http://gb.archive.ubuntu.com/ubuntu/ hardy-updates main restricted universe multiverse

## UBUNTU SECURITY UPDATES
deb http://security.ubuntu.com/ubuntu hardy-security main restricted universe multiverse

If you wish to enable the backports and proposed repositories as well (recommended), then add these lines as well

## BACKPORTS REPOSITORY
deb http://gb.archive.ubuntu.com/ubuntu/ hardy-backports main restricted universe multiverse

## PROPOSED REPOSITORY
deb http://archive.ubuntu.com/ubuntu hardy-proposed main restricted universe multiverse

Now save and close the file, and then reload new source list using the following command

sudo apt-get update

If that command runs with no errors, then you have successfully enabled the universe and multiverse repositories.

via: http://www.ubuntugeek.com/how-to-enable-the-universe-and-multiverse-repositories-in-ubuntu-804-hardy.html