I have found sometimes it is necessary to plug in w USB (I was trying to add as shared network printer on an XP machine), what i have found is that for whatever reason the only way I can get it to add correctly is by browsing the network and connecting to the printer that way (open remote computer and when it shows shared drives and printers double click the printer). I could never get it to add or find a driver when i used the regular add printer method from Devices and Printers.
Hope this helps someone.
C