For the benefit of future starters:
I don't know whether it is something specific to my network (Cisco router with a 24-way switch before the Webbricks) but trying to access 10.100.100.100 from my web browser only gave "Server not found").
The solution was to use WebrickMon.exe (fior each Webbrick at a time) which is great for morale as it confirms existence of the Webbrick on the network, and then change the Webbrick address using the input field at the bottom to 192.168.xxx.xxx
Maybe someone could reply with a guide to suitable IP addresses to use for ones Webbrick network.