I'm running Ubuntu 12.04 with the classic Gnome desktop and the above help didn't work for me.
What I ended up doing was (all through the terminal):
1. Using the terminal add the correct software source
2. Add the key:
3. Update the software sources
wget -O - http://www.bchemnet.com/suldr/suldr.gpg | sudo apt-key add -
4. Look for what driver number your printer needs on this page:
sudo apt-get update
5. Install the driver in a terminal
(replace the last number with the driver you need and found in 4)
sudo apt-get install suld-driver-4.00.35
Now installing the printer through the normal 'add printer' dialog works fine.