OSCommerce - Add Paypal IPN

I am not receiving some of the orders that are paid for threw paypal. I am using paypal Auto return but customers are clicking off the page prior to returning to the OSCommerce site. I have read on the OSCommerce forums that Paypal IPN will fix this problem but I have trouble following the instructions to set this up. IF this is what fixes the problem, I need this installed so that I can test orders that come threw the store. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). ## Platform OSCommerce