Problem fixed.

I gave up in the end for fear of doing more damage and handed it over to someone who knows what they are doing.

It turns out that for some reason, the /etc/fstab file was completely empty (so where it was complaining about a particular field being missing, it was because there was actually nothing there at all). Apart from making files difficult to access properly, this interupted the boot process and so a whole load of other things weren't working correctly either.

After adding the main linux partition to fstab correctly knoppix managed to fix the rest itself at the next reboot.

Lesson learnt: Make a backup of /etc/ to replace settings should this happen again.