Mariano Gomez has a nice post on using the Win32 common dialog box AP to return a file path to a Dynamics GP modified form field.
Mariano includes lots of screen shots and step by step instructions so don’t be intimidated by the cool title.
Returning a File Path to a GP Modified Form Field
Archived post from 2008. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.