Thanks, John & Al:

I did get a driver from one of the afore-mentioned sites, and it wouldn't install unless I was in "real-DOS mode". Going into that mode is possible: but it looked a bit hairy, and with no guarantee that the down-loaded driver would actually work, I'm staying with plan (f) for now. (I also tried the threatening it with an open upstairs window, which was even more successful than all my other attempts. Alas, not successful in an absolute sense.) Plan (h) is buy a new machine. (It's all my brother's fault: he bought it for my mum, who found it surplus to requirements: but that's another story. She needs a new operating system, now.)