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).

QuickTime is more than just simple video. Apple’s multimedia architecture can marry many forms of media–video, sound, text, still images, and animations made with Macromedia Flash. QuickTime movies ...

Feelorium has announced the release of Tattoo 1.0. It’s a QuickTime media skin editor that runs natively in Mac OS X, and it enables QuickTime developers and media producers to provide their users ...