Computer disaster question

[FM WarB]

My playtest opponent's computer died and he had to buy a new one. We were playing our new Campaign Waterloo Four days in June scenario without the latest update, as neither of us had Vista at start. Now, he will have Vista with new computer.
Does he need latest update? Can we play with two different update versions of the game or can he play with older version, which I can send him? Can he or I, or both upgrade mid game, or do we need to?
His computer disaster happened just as night was starting 17/18 June, and it would be a shame not to finish it.
I have noticed, with recent download of Campaign Wagram latest update, that it runs ok sans Vista.
Help!!!