Lets do it the easy way. Find your printer on the network using the desktop.(you stated the printer was jacked to the desktop via usb or parallel port I assume.) Right click it and select share. Now name the printer that is shared. Every computer behind the firewall(router) will be able to print to the shared printer. Example: Find a document in word ..using the laptops or top. Print the document. A screen will ask what printer to use. Remember the shared printer you named. It should show in the list of printers. Select it and use as the default printer for that laptop or tops. Have a great day !
The printer can be found using control panel on the desktop

when beginning the share process....flat