The PayPal_IPN class provides an simple way of capturing the PayPal IPN POST data, confirming it with PayPal and then making it available to the application.

The IPN Class can be downloaded from GitHub below.
http://github.com/ArthurGuy/PayPal-IPN

The example code below shows what code you would need to make use of it. The code would be placed into a PHP file which would be specified as your IPN destination within PayPal. After the 3 lines you can the extract the returned payment data from the PayPal object.