LLR

I have got the following problem with some Clients in my Windows 2000 network: If somebody just clicks a Quicktime movie once, the explorer tries to show the movie (like it does with picture etc.). Then the explorer.exe crashes... And it doesn't matter if there is Quicktime installed or not. It's a strange behaviour, because I never had the problem before. Does somebody know where to disable *.mov files from being shown by the "Active Movie Window", which is responsible for showing the video preview in explorer? I looked at the registry, but I am not sure if I found the right keys - so I just don't want to try it out and delete them. Thank you in advance for your tipps and hints, yours LLR