It looks like UW has QuickTime installed and that is why he and I can both play these movies.
If Windows people have QuickTime installed, many do now because it is part of iTunes, which player does the browser use for playback of mpegs? Do they have a choice? What are the defaults?
I personally really would love to use
mpeg-4(.mp4) instead of the mpeg-1(.mpg) vids at the paysite that I manage.