I needed to have a user easily enter a latitude and longitude where there might not be a true address, so I created a simple script to populate form variables when a user doubleclicks a Google Map.
The function that is fired in a dblclick event will then set the 2 form variables and leave a marker behind to help the user know where they clicked.
You will need to change the center points and the form names, but all this could be dynamically set as well.
Hope you can use this in your apps.
Note: you will need to fix the 2 InvalidTag's with script.