Although its possible to set up some kind of anti-leech script which could provide some protection from direct download, it is really a moot point.
if your videos are "streaming" out of /images/stories/videos/, the videos are playing back using "progressive download". As the video is being downloaded, it pseudo streams by starting playback on the file before the whole thing has downloaded. This is why videos some time buffer, because the file plays back faster than it downloads, so you reach a point where you need to wait and let more of the file download.
I say all that to say that after the video completes downloading/buffering, the video is sitting in the remote computers internet cache already and can easily be recovered by going to c:\documents and settings\<current user>\local settings\temporary internet files\
Even putting your files on a real streaming server isn't 100% protection any more with programs like replay media catcher -
www.applian.com/replay-media-catcher/ which I have used to download files from like hulu and cnn... supposedly the "undownloadable files"