prevent duplicate form inserts-ms Access 2003

Hello all,

I am creating a simple asp .net form that inserts the form data into an
MS ACCESS database once submitted. What I need is to find a way to
prevent duplicate submissions by checking the database if the same data
had already been submitted, and if a duplicate insertion is being made,
to prompt the user "You have already submitted your information".

How can this be done?

Thanks!