Sorry for the late arrival of key info.
As my last mail suggested, I can ping various addresses including your suggestion of pinging PPRUNE - but only by using the IP address - not the name. Using the physical address in the browser address bar does not elicit any response.
The only thing listed on the connections page is the broadband adapter itself, and I've selected the option "always dial my default connection". There's nothing selected in the LAN settings dialogue box.