OS-X Snow Leopard (10.6) does not have the correct printer drivers available to print to the Library printers. You must download and install the correct drivers before adding the printers. Alternatively, upgrade your operating system to OS-X 10.7 or higher.
Once you have downloaded the drivers from the links above, here are the steps you should follow to install the drivers. Note: You perform these steps for both downloaded files if you will be adding more than one printer.
Now you may add the printers to your computer