certainly not in iWeb itself.
You could add an HTML Snippet with an image link to the movie
<a href="URL of the movie"><img src="URL of the image"></a>
so when people click on the image the movie will load but that's probably not going to work for people using IE.
Otherwise you would have to use a player like this one:http://www.longtailvideo.com/players/jw-flv-player/
but you would also have to convert the QuickTime movies to something else for that.
I currently don't know any other way, if you find out please tell me.