Creating GPI files

I finally got a test point working last night using gpx and mp3 files. Of course there is always more testing and developing to do. What program do you create GPI files in? My new copy of Mapsource does not save to that file format and none of the gps programs I have read it. The Nuvi I have came with a pre-loaded poi.gpi file but no way to edit it. I am sure I missing something simple.

I loaded some gpi files from here. Very cool but have a few things on my wish list.
+Markers on the screen to show an overview of where the points are (think this is currently possible just haven't worked out the details.)
+The ability to stop the tourguide.mp3 file that is playing.
+Turn the tourguide off.

Thanks,
Mike