Did you install the printer software on BOTH computers? Sometimes the standard Windows drivers which are installed when "adding" a printer just don't get it done.
Hope this helps.
I network my HPPavillion Desktop and my IBM 600E Thinkpad. I have activated "sharing" on both computers to share the printer connected to my Desktop. Each time I go to use the printer from the laptop, it goes through all the functions (icon comes up then disappears) except to print. It recognizes the HP Deskjet as the default printer but will not print