If you go to one of these sites that tests your firewall,
http://www.dslreports.com/scan
( for example )
you will find that IP-Cop defaults to opening port 113, but not to your LAN, but to itself for some strange reason. It can be turned off by going to the Firewall tab, external access tab and unchecking the tick under "action". See page 41-42 of the Admin guide for further details.
I am currently using IP-Cop but it doesn't allow total stealth as it replies to pings, this requires some editing of the firewall files.
Smoothwall however had a facility to do this from the gui, and in some ways I think I may change back.
floppy