Naturally, after I posted, the requirement changed from .xml to simply viewing the .mpp.
With that, I flat out cheated...
I made a Page Viewer Web Part that points to:
http://housatonic.cloudapp.net/Views.aspx
It works well enough, except that our SharePoint Portal uses smartcard authentication, which the reader can't process. This means that the user has to copy the .mpp to their local machine, then open it in the viewer. Other than that... WORKS
GREAT!
Steve Clark, MCTS | Twin-Soft.com