Well, I'm making progress.
Restoring the original configuration was painless. And seemed to take only a few minutes. The hard part was finding out how to do it! Silly me for thinking that I should use the "Recovery Disc" that came with the PC. No, I needed the "Application & Support-Disc". The "Recovery Disc" is used to either repair the existing installation or to replace it with a completely new installation. Nice one Medion. No documentation with the PC or on their web site of course. A README.TXT on the recovery partition would have been nice too.
Anyway, after several hours installing them one at a time, I managed to get all of the updates installed. One at a time because I have previously fallen foul of a known issue with Vista becoming unusable when trying to install multiple updates. Only one gave me an issue - the .NET 3.5 framework installation failed first time, but succeeded on the second attempt. Vista SP 2 was the last to go on - I did not even get offered that until all the other updates were installed.
SU 7.1 Pro was the first app that I installed. It went on straight away, no problems.
A long weekend now getting all my other apps on and validated, then several hours re-installing the data. Don't you just hate computers?