I'm back in XP Pro now. All is well, although I have to be here to tell it to start that, rather than Win 7. Next job is to reinstate Grub, which will sort that. MS doesn't seem to recognise the existence of non-MS boot utilities
The connection to the router is there, and working fine. I can browse the web and do all that stuff. It's just that Win 7 won't let me tell it what the network is called, or how to connect to it. It's called "WORKGROUP", has a gibberish computer-designed password that must be used, and all the other machines have to go its way. Or, in this case, not.
Time to play. Somewhere in the depths will be the place where the network name and settings can be changed. Or Mr Microsoft has a problem. In the XP days, the network was called MSHOME but could be changed.