Brought Gadget back with me from work to get it working again. After some tweaking, twiddling and frobnicating, he got a working setup going again. However, when he went beyond that and tried to get DHCP and DNS working, he encountered problems. After about an hour he gave up, leaving Jessica with DHCP (ie IP addresses allocated dynamically from a bucket) but a hard-coded DNS, although it is now on the ADSL modem. Later, I set Hilary up the same way.
This will probably not be the last post on this subject.