I don't think you understand how Instant Payment Notification works. The customer should never hit the paypal_notify.php page.
When the customer completes a transaction on Paypal, Paypal's servers POST details of the order to paypal_notify.php. Assuming everything is kosher, your site will update the order status and send out the emails -- at least it should.
If you're geting blank addresses in the order email, it's because (I think) the code is calling an incorrect function. To fix this, go here:
http://www.oscommerce.com/forums/viewtopic.php...p=170917#170917
If you're not getting emails at all, make sure "Set Orders Status" is set to something other than 0 (in my store it was set to "default" which equaled 0). This will cause orders not to be completed.