We listed the steps for creating a desktop printer in 10.5.X in Barkings! back in 2008. Doing so allows you to print a file simply by dragging and dropping it onto a printer icon in your dock, eliminating the need to launch an application before printing it.
Those steps in Snow Leopard and Lion are no longer valid. You can add the functionality of a desktop printer to your dock with the following steps if you’re running 10.6.8 or later:
1. Open System Preferences on your Mac.
2. Select the Print and Fax preference pane.
3. Double click on the printer in your list and it will open up the printer as an application in the dock.
4. Control click on the printer in the dock and select Options.
5. In the Options menu, select to leave the printer in the dock.
Now that the printer is in the dock, drag any document over the printer and, when it darkens, release. The document will print without opening an application associated with it.