I am on workgroup with my printer connected directly to my XP pc. I have no problem printing from the XP pc but can't print from my laptop and another pc that runs windows 7. All the computers on the network can see each other and have no problems with file and data sharing.
From the other PC's (excluding the XP machine), when you connect to the XP machine, are you able to see the shared printer? Have you tried deleting the printer from the other machine's and reinstall them? Also after deleting the printers, I would run ccleaner and make sure the registry entry's are cleared as well... Then connect and reinstall the printer.
Also, any error's when trying to print? If so what do they say?