Here's a video of a continuous upgrade from ms-dos through every windows version all up to windows 7 (a timespan of ~20 years) that proves it's possible. http://www.youtube.com/watch?v=vPnehDhGa14
The whole time I was watching this I was thinking, how would I explain to a normal human being why it is that I can't look away. Windows 3.0 especially took me back to my adolescence, like a smell.