I have peen programming in PHP since V2 PPH/Fi, about 12 years, have a masters degree in Object Oriented Sofware Engineering and have been senior Sofware Engineer for one of the largest ISPs in Europe. I have a lot of OSC experience.
I presume you mean a paypal chechout button so the user does not have to log in and not merely the installation of the Paypal IPN module.
I'm also assuming you already own a copy of Live Support