prevent reporting an event twice

Hello All,

                 Is there any way to prevent user from reporting an event twice.  for e.g. a user enters a set of information while reporting an event. Next time he can report the same event again.

                 Also customer requires that the information that he has already entered for a handler while reporting an event , if he goes back and reports the same event again then those information are pulled in the event reporting screen in an event handler.

Thanks,

Shubh.