Take that, you horrible little computer. Play up on me, will you? Well, we saw about that, didn't we. Now you're singing a different tune. :evil:
Yup: the fresh install did the trick. I used Windows 95 this time, instead of W98SE. Not that that was the reason, I don't think. I think the problem was that it's a horrible little brown A-Trend board, as nasty a pile of electronic turd as have ever been built around a perfectly decent MVP3 chipset. A-Trend, of course, are yet another of the phoney names PC Chips think up for themselves, or so I believe. Certainly, the qualities of those A-Trend ATC5200 boards live up to the PC Chips reputation.
This particular one, I think, has something nasty going on with its PCI bus, such that it's loading the PCI NIC drivers no problem, but failing to initialise things properly. I used two known working Realtek cards, an A-Open and a C-Net, and though they showed up just fine in the device manager, and would talk to the network, neither one would TCP/IP, even when I asked nicely. The USB thingo is up the spout too: something about "Windows has disabled this device due to excessive bus retries".
But the third clean install with an ISA NIC has done the trick and I can now fold away at the lightning pace of a ... er ... a K6-2/500.
Um ... Why did I bother?