Get key for the data just inserted into db

I am creating a registration form for a website. When the information the user enters into the form is verified, it will be inserted into a table (tblStudent) in a MySQL db. The primary key of tblStudent is an autonumber. Is there a way to get the primary key for the user I just inserted into the db? I need to set the primary key for that user to a variable because I need to pass it along to paypal for an IPN script.

Thanks