Not sure what you mean by "mainstream quicktime video's". If a QT video appears on a website, the author can choose to prevent it from being saved on the user's hard drive. Once the video loads, you can click on the little tiny arrow at the right edge of the controller bar (or right-click/control-click on the video itself) to see if the "Save as QuickTime movie" option is available If the video is truly streaming from a server, it won't even appear as a complete file in the Temporary Internet Files directory, just a stub that aids in the playback. This is one intentionally where authors want to control their content. The only solution in that case if you must grab the video is to use software that records what's being displayed on your screen - or else point a video camera at your monitor!