I will try the troubleshooting and QuickTime reinstallation this weekend, though I think its not a QuickTime issue because resetting Safari solves the issue. Actually I am confused as to what it is, given that movies from some other sites play. However, I wouldnt go as far as erasing the hard drive..would rather watch the trailors on my old Vaio or TV
Another thing which might give a hint to some experts here: When the movies do not play, they do not work in Safari, iTunes, QuickTime and Camino (all of which share some settings?). IE, on the other hand plays it fine (because it has its own settings?). I am not sure about the settings part as I am new to Mac.