What is the format of the uploaded video? Remember the web browser has to have the ability to play that format of video.
When I add a video (type MOV) I add a jpg of a frame of the video and set the link so if you click the picture, a new window opens and the video plays.
Here is the code that was in the post which you can see at http://zenofmud.org/archives/250
<!--Mime Type of File is image/jpeg --><div class="postie-image-div"><a href="http://mydomain.org/wordpress/wp-photos/20080415-070945-1.jpg" onclick="window.open('http://mydomain.org/wordpress/wp-content/uploads//2008/video/GregEllenweb.mov','full_size_image','toolbar=0,scr ollbars=0,location=0,status=0,menubar=0,resizable= 1,height=489,width=659');return false;"><img src="http://mydomain.org/wordpress/wp-photos/thumb.20080415-070945-1.jpg" alt="willyou.jpg" title="willyou.jpg" style="border: none;" class="postie-image" /></a></div> But if you click on the picture, you can see the video.