560956 PHP Paypal IPN Script

I currently have a registration process where an individual can create their account, In Example : Email, First, Last Name, Etc. The data is submitted to the database with all the correct information provided. Then the user is prompted to signup for the service. There are (4) Paypal Subscribe buttons. -- I need to be able to take that user from that registration process (which is not completed) to then click on the Paypal subscribe, after clicking on this it will bring them to paypal so they can purchase the service. Upon successful completion, I need them to be redirected to a confirmation page. At this point we should be using IPN to inform my site that the user "paid". I need the script to know which user this payment was for and update their registration within the MySQL database from "active = 0" to "active = 1" and the subscription they chose "subscription = 1 or subscription =2" etc.