I think what you need is MIME types. Look at /opt/QtPalmtop/etc/mime.types
Also, then, if you open up the .desktop file for the app that is supposed to run the file, you\'ll find the association of the app to the mime type, as well as a reference to the icon to use for the file.
The .desktop files are in /home/QtPalmtop/apps/FOLDERNAME/ where FOLDERNAME is the tab in Qt that the application is in.
Hope this points you in the right direction. I\'ve done it before, but I just stumbled through it until it worked. Someone else may have more complete instructions.