Run this command for Ubuntu 8.10 (I had to make this 2 lines but it is one line)
sudo wget http://www.medibuntu.org/sources.list.d/intrepid.list --output- document=/etc/apt/sources.list.d/medibuntu.list
sudo apt-get update && sudo apt-get install medibuntu-keyring && sudo apt-get update
You may be asked to accept this package even though it cannot be authenticated. This is normal; typing "Yes" means you trust Medibuntu.