Hi Phillip,
You could do this using Visual Basic for Applications, the scripting back end of Microsoft Office. You would need to code the form to capture the latitude/longitude, create a KML file on the fly, save it, and then use the shell to open the file.
If you're looking for more direct control, you probably want to look at the
COM API, using Visual Basic or VBA (I'm not sure if VBA would allow you to do this).
ManoM