It should be straight forward Clive.
When you set the network up did you set it to allow file and printer sharing or just use the router with no file sharing at all ?
If its set up with file and printer sharing then open the printer folder on the pc that its installed on, right click on the printer icon and select the share option.
If its not set up for file and printer sharing then run the network wizard on both pcs again.
Select the option "This computer connects through another pc or a residential gateway" then enable file and printer sharing.
At the end of the wizard select "Just finish the wizard" then run the wizard on the second and subsequent pcs