Ubuntu 8.04 "Hardy Heron":
sudo wget http://www.medibuntu.org/sources.list.d/hardy.list -O /etc/apt/sources.list.d/medibuntu.list
Ubuntu 7.10 "Gutsy Gibbon":
sudo wget http://www.medibuntu.org/sources.list.d/gutsy.list -O /etc/apt/sources.list.d/medibuntu.list
Ubuntu 7.04 "Feisty Fawn":
sudo wget http://www.medibuntu.org/sources.list.d/feisty.list -O /etc/apt/sources.list.d/medibuntu.list
Ubuntu 6.10 "Edgy Eft":
sudo wget http://www.medibuntu.org/sources.list.d/edgy.list -O /etc/apt/sources.list.d/medibuntu.list
Ubuntu 6.06 "Dapper Drake":
sudo wget http://www.medibuntu.org/sources.list.d/dapper.list -O /etc/apt/sources.list.d/medibuntu.list
Then, add the GPG Key:
sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update