I decided not to take the hammer approach (), and to turn off the UAC.

This was more difficult than I expected because this is a French Language PC, so lots of basic stuff is spelt differently. I also turned on the hidden administrator account.

In case anybody else is in the same dilemma, not too familiar with techie french, here is how I did it (English version in blue).

1. Turn off the UAC

Simple. Download and run this Disable Annoying Vista UAC popups with TweakUAC (free!)

It is free and it works.

2. Turn on the hidden administrator account.

Find the command prompt. It is probably pinned to your start menu, but if not then try Démarrer --> Programmes --> Accessiores Start --> Programs --> Accessorees and you will see it there.

Right click on it and select Exécuter en tant qu'administrateur

You will get the black DOS window

Assuming that the password you want for your administrator account is MAckem99, Type ...

Net user administrateur MAckem99 and hit enter
Net user administrator MAckem99

You will get a message confirming successful "termination" of the command

Then type

Net user administrateur :active:yes exactly like that and hit enter
Net user administrator :active:yes

You will get a message confirming successful "termination" of the command

That's it folks ... test it out with "Change user" and you will see the administrator account ready to log into. You can do so with the password MAckem99