IPN is not a program. IPN is a feature Paypal offers to developers. With IPN, when someone pays you through paypal, an HTTP CGI post is initiated to the URL you specify. This URL would be some code; PHP, ASP, JPS etc, that you have had written that can receive that HTTP post, parse it, and do something useful with it. Sounds to me like you need to find yourself a developer to code an IPN page. What kind of webserver do you have? Linux or Windows?