This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
I don't know what a "pen drive locker" application does, but where does the user click on a drive symbol - in a window of the file system, or is this something your applet shows? If the former, then this isn't possible. Applets can react only to events inside of the applet GUI.