I hope I’m not speaking too soon, but things are looking up. I got a SATA power cable and a floppy drive from the local Maplins, and I’ve got a fresh install of Windows up and running.
Even better, I ran Samsung’s low-level diagnostic utility (HUtil) on the faulty disk, and it was passed most of its tests successfully. The surface scan looked like someone had used the disk’s platters for serving up a buffet lunch, but it was still mostly readable. In fact, I’ve got it mounted now, and busy copying off all the data I can get.
Lesson learned: backup, backup, backup. Disk failure is not a matter of “if”, it’s a matter of “when”.