There are several threads in Apple's QuickTime Discussions Board citing problems playing QuickTime movies in Explorer, especially the movie trailers on Apple's site (see one and two, for examples).

Several readers have reported an issue where embedded QuickTime content on Web pages will not play properly after the update. MacFixIt reader Mark Feldman writes: "After updating to QuickTime 7.1, ...

^-- see above... i absolutely abhor quicktime, and i can't stand installing it, but i have a few funny clips, and some shorts and movie trailers that i can only find in .mov format (like the whalebomb ...

But now I notice that the audio is pretty quiet (both quicktime and videolan). Let me put it into perspective. When I crank the ibook all the way up with my headphones it is fine to sit in a quiet ...

At some point, most Mac users have probably whiled away a few company minutes watching Apple’s QuickTime movie trailers. But QuickTime can do much more than just bring you the latest Spider-Man 3 ...