Hi again - just got fixed!
I got the Zoom X5v (couldn't resist the VoIP thing), and I just set it up as an ethernet-connected router. Smoothwall was happy about it, all I had to do was log in as root and run the setup command again. All my log files etc still intact!
Smoothwall doubly happy, since I now get NO entries in the firewall log file! (the Zoom has a built-in hardware firewall). I get some weird messages in the intrusion detection log, so I'm off to the 'snort' homepage for explanations.
Question: do I need a smoothwall if the Zoom has a built-in firewall?
Anyway, thanks for all the responses.