If you want to be able to print just by dropping a document on a desktop printer icon without launching an application, you first need to make the icon appear on your desktop. It is done this way:
Go under the Apple menu, under System Preferences, and choose Print & Fax. When the preference pane appears, click on the Printer Setup button, and when the Printer Info dialog appears, press Command-L to show the Printer List dialog. Your printer will appear in this dialog. Click on it, then go up under the Printers menu (in the menu bar) and choose Create Desktop Printer. A standard Open/Save dialog will appear asking you where you want to save it, usually on the desktop. Click Save and an icon for your printer will appear on the desktop.
Then just drag and drop a document on the icon and it will print.