Bentley Viewer and IE incompatibility?

Hi,

My organization has Bentley Viewer, on Windows 2000 clients, for viewing
Microstation *.dgn files stored on our web server. We currently use
Netscape 4.77
as our browser. The user simply navigates to the .dgn URL and Netscape
downloads
the file and opens Bentley Viewer as a standalone application for viewing
the file.

No such luck with Internet Explorer 6.x. (on which we're soon to
standardize).
When the user navigates to the .dgn URL, IE either displays a "broken image"
link at the upper left of the IE browser window or gives a strange error
about
it can't or won't send the file. Some background:
-- I've checked the file associations and everything looks good
-- The MIME type appears to be image/vnd.dgn, unless I'm mistaken
-- We're using IIS with ASP/VBScript
-- I've tried setting up IIS to have the MIME type for .dgn files but
that
didn't fix anything

In short, it worked great on Netscape but won't on IE. What do I need
to make this work on IE?

Thanks,

Patrick