Since the old desktop box is definitely dead, I just got around to sticking its memory into its replacement. So now I have my biggest ever desktop, with a full gig.
It works. But somehow, the hardware change upset linux’s (ACPI) hibernated state. That’s a full power-down with save-state-to-disc, not the kind of semi-suspend that’ll wake on things like keyboard or LAN. Not only did it not do a rapid boot to the same state I had before; it went and fscked everything!
Anyway, it all works fine now:-)