Well, Saab Dastard, by mentioning upgrade to new firmware as a byproduct of which settings would be reset, you gave the catalyst to solving the problem because this caused me to remember the "reset pip" on the back panel. After resetting the router this way, during which period it remained powered up and with both my laptop and the ADSL modem connected via ethernet cables, I confirmed that ethernet web browsing still worked.
With ethernet still connected, I then enabled a wireless connection in parallel and used ipconfig/all to check my IP addresses. Hmmm... Not only did I have two addresses but they were in a different range to the router (192.168.1.2 and 192.168.1.3 versus 192.168.0.2 and 192.168.0.3 that I expected from the Netgear router)
Perhaps, methinks, the ADSL modem *does* have a DHCP server after all, so I connected to the Netgear admin page and did two things: Firstly I changed the Netgear router to an IP address in the same range as the ADSL modem and high enough not to ever likely be allocated by the modem's apparent DHCP server. I chose 192.168.1.100. I left the subnet mask alone at 255 etc. The second thing I did was to switch off DHCP on the router.
After RMB "repair" on the wireless connection of each PC in the house, everyone then had wireless access to the internet.
Yay! :-))
A couple more minutes later I had set up security, so off we went.
Everyone's more than happy and a cold Staropramen Svetly is coming my way shortly. Na zdravi (Cheers!)
Grateful thanks for the help and pointers along the way.
XV105