QuickTime player is not reliable for previewing movies. Not unless you have the appropriate codec/plug-in such as divX or others. I've suffered the same identical problem as you with QT player but when I previewed the video with VLC, no such problems. Get VLC here: http://www.videolan.org/vlc/ (choose nearest mirror site)

For LW support (they don't use phones there, they use mirrors or smoke signals lol ) use service@limewire.com to email them.