The best thing to do right now is for you to compare your iMac software and hardware with your wife's iMac to determine what differences there are. That should help determine where the problem is.
Also, which games are you referring to? We have Virtual Villagers 1: A New Home, Virtual Villagers 2: The Lost Children, Virtual Villagers 3: The Secret City and Virtual Villagers 4: The Tree of Life.
Since we are working on this problem here, I will email you that I have replied here on the forums, but it's best to keep the problem in one place.