The BIOS won't ever recognise the drive because it's larger than 38Gb. It wasn't a problem for Windows, and it's a secondary drive so I'm not booting off it.
No, probably ancient...
I'm going to take the drive down to a friend with a fast (and modern) PC who can do the tests more easily.
To be honest, I think the whole thing is simply falling apart from old age, but it may be just the the drive. Of course, I've been a little negligent with my backups lately, and I risk losing over a week's data... Always the way, and there's nothing critical, just photos... :(
Thanks for the help, guys (and gals!)