Herbert,
Pardon me for stating the obvious, but if you
only want the action to fire if the user manually manipulates the combo box (with the mouse)
then wouldn't a "MouseListener" be more appropriate?
http://java.sun.com/j2se/1.4.1/docs/api/java/awt/event/MouseListener.html [You can use the "addMouseListener()" method that "JComboBox" inherits from class "java.awt.Component".]
Hope this helps.
Good Luck,
Avi.