Steven,
Okay, the critical file is the
http://pldaniels.com/downloads/ipnrx-php.txt file which you have to tell PayPal to request (you choose the URL when you create the button).
The normal receipt file that people see is something like
http://pldaniels.com/downloads/pprebook-php.txt
If you need more info, just holler - the one that is the trickiest is the ipnrx one.
Both files are skeletons but the key in the ipnrx one is that it opens up the SSL/https backchannel to PayPal to validate the transaction for you.
Paul.