Thanks Steve!
That would explain all this certainly.
I'm very happy to re-read the page you linked to that shows that ad0 error can be ignored- I was yet to go back and check that was exactly what mine was reporting.
Up until now have been having trouble getting the WAN port to pickup a routable address from the bridged cable modem/4 port switch. Any of the pfSense's hosts' Intel NICs will happily pickup an IPv4 address if I connect them to a network with a DHCP server, but when I connect them to the cable modem's 3rd or 4th port it won't. It shows a link light and negotiates speed & duplex- but won't bring up an IP connection. I've tried assigning WAN to other ports, manually setting duplex to Full and Half. Other devices on my network pickup a routable address if I plug them into the cable modem instead of the pfSense host (LATER EDIT: but only ones which have been conected to it before)
In the end I read in another post that this is expected behaviour with cable modems/networks. After re-booting the cable modem it came up fine. Had some weird things happen during all this with the dhcpd/local interface after completing the webgui's config wizard. Couldn't regain access from the LAN and had to reboot a few times. Maybe my Netgear gigabit RTL card is not getting a warm welcome (it worked well under m0n0wall).
Anyway… thanks again. Finally it is time to try the lusher pastures over here at pfSense!
On the way home today I found a better rig to use- thrown out in the street just like the old one. An old AMD Sempron 1800+ powered Compaq desktop PC. It has better BIOS configuration screens- and the CPU is a 25W thermal design rather than the 65W Pentium D. The RAM from the old box fits, so now I have 2GB and after disabling all the unused hardware/interfaces such as Audio,I/O, etc. much faster boot and a bigger LED to tell me its on. Yay!