We use the following approach:

1. Unzip Mason to a convenient location 
2. In Eclipse, create a Project for Mason, maybe "MasonTools"
3. In the Mason folder series, copy folders "sim" and "ec"
4. Paste them into the "MasonTools" Project
5. Right click on a project you want to use with Mason
6. Click on "Java Build Path", then "Projects", then select "MasonTools" and
close the panel

This allows you to control access to Mason easily. It also allows you to see
the Mason source code. You can even copy and paste into the Project the
"sean" and/or "docs" if you want to see the html documentation on your
viewer (though I usually use a shortcut icon to the documentation index).

You will get error warnings unless you have properly installed JMF and
Java3D. 
  
Let me know if you have any problems.

John
 
John W. McManus

If I cannot build it, I do not understand it. -- Richard Feynman, Nobel
Laureate