Counter to Display Number of Registrations available

We are looking for someone to design a counter to be displayed overlaying a banner image on the home page. The counter must countdown from 100 to 0. Each time someone registers for our seminar we want the counter to show 1 less registration available. For example, on the homepage you will see an banner image that says "Only 100 Registrations available. Click here to register" Once a visitor submits his registration form the counter on the home page would then say: Only 99 Registrations available. Click here to register And so on and so on until there are 0 registrations available. For more see the website [login to view URL]