First thing to know:

 In Microsoft MovieMaker, the working file is not the final film.  The final film needs to be compressed and saved in a new format in order for you to see it. 

Second thing to know:

 You can tell whether a movie has been compressed by the extension. In your libary, a working file might look something like this:  Book.mswmm.  Once it has been saved it looks like this  Book.wmv

Third thing to know:

The default drive for saving the .wmv file is called SharedVideo and it's on the C drive.  You can't access the videos from there.  Nor can you save videos to the share folder... They must be saved where the student has all their assets... their individual MyVideo folder.  After they have saved the videos the proper way, you can pull the .wmv files into share so you have access to them from your login for evaluating and publishing.  It sounds complicated.. but it isn't.

Watch this powerpoint for step by step visual instructions for how to save your movie the right way