Even trying to use the hidden recovery partition didn't work (installation CDs? what are they?) this time, so a decision was taken to install Win2k on it as we do have a CD for that.
As the main partition didn't think it had been unmounted properly (it hadn't) this meant installing it on the hidden partition = a couple of minutes with PartitionMagic 7 to unhide it, and half an hour or so installing Win2k+SP4.
I'm now in a position where I can read most of the directories on the main partition and run the Win2k repair utils on it. But not the three directories I created on it before the problems and which have things I want to access on them.
I do not remember setting sharing restrictions on them, but it's not impossible that I did. I do have an account on Win2k that's the same username and password as the one that would have been used... and that can't access them either.
So, what should I try? Converting it to FAT32 isn't an option as PM7 thinks it still hasn't been properly unmounted.