First, make sure that the Network Trust Level and the trust level of the printer are set to "Shared" in the Norton Network Security Map on the XP machine.
The printer is set to 'Full Trust' per the Network Security Map --not sure where to 'see/set' "SHARED".
As far as I an tell all Norton settings on both XP machines (as well as the W7 machines) are all the same. But I don't know where/what to check regarding the specific port settings.
The supplied printer s/w was indeed installed on the XP machine (as it was on the other XP machine and the W7 machines --yet it does not work on the one XP machine.
Still looking for help with ensuring port 9100 is open.
Glad you got it working. Either "Shared" or "Full Trust" should have worked. "Shared" allows certain protocols used in local networking, such as UPnP, which makes it easier for devices on a network to find each other. Other traffic is monitored with the same rules that are applied to incoming internet traffic. "Full Trust" allows all traffic from other devices on your local network, and so is somewhat less safe - you want to make sure that no infected computers are on your network.