Well...if you had those users store their Autotext and AutoCorrect in a template other than normal.dot, you could simply load that template. But, I doubt this happened.
You mention upgrading. However, you did not mention what that was! Is this a change to 2007/2010? if so, later versions deal/handle Autotext fairly differently.
In any case though, you will likely have to use the Organizer and recreate them.
This is another reason why using global templates other than Normal are very very handy.
Gerry