How to create a new MIME type for a Sugar activity?

[James Simmons]

I am writing a Sugar activity in Python.  This activity will enable the 
user to navigate through a list of image files stored in a Zip file by 
using the arrow keys, and might support a slideshow feature too.  There 
might be a hundred image files stored in the Zip file.  Grouping the 
images in one file makes it much easier to deal with them in the Journal.

The thing is, I want this Zip file to have its own MIME type, so that:

1).  The Etoys activity does not try to open the file, at all, ever.  
EToys takes a long time to start up and shut down and it is really 
annoying when I open the file with EToys instead of my own activity.
2).  My Activity *does* open the file.
3).  The Zip files containing images show up in the Journal with my own 
Activity's icon, which looks like a slide projector.

To accomplish this I have created my Zip files with the extension 
".slides" and I'd like to be able to use the MIME type 
"application/slides" for such files.

I'm also interested in creating a reader program for Gutenberg etexts.  
I'd like these files to have their own MIME type too so they don't get 
opened by the Write activity by mistake.  I was thinking of using a file 
suffix of ".book" and a MIME type of "text/book" for these.

I tried using a mimetypes.xml file in the bundle but that didn't work.  
I couldn't find an example of an Activity that used such a file so I'm 
not certain I'm doing it correctly.

I'd appreciate any information on MIME types or on alternative 
approaches that would solve problems 1-3.  Thanks much,

James Simmons