this is a quickie: i have a site which uses paypal IPN to allow users to subscribe and pay for subscription membership. i also have a calendar at [url removed, login to view] which users can schedule appointments. i want to alter the (PHP) calendar so that users first have to make paypal IPN payment for an appointment before it can be scheduled. if you know php and paypal IPN, this should be a cinch! i already have IPN working on my site, just need to add functionality for scheduling appointments.