PayPal IPN Script work

I need someone who is knowledgeable of the IPN requirements. I have the return script from their example integrated into my return page, I need some error checking for duplicate transaction work, then I need someone to itemize step-by-step and help me get it working. I have reasonable skills and can handle my end. I do need to get IPN working, I have the dollar amount to pass Paypal from my program with the persons name who is paying. I also need to pass a second string (name) and have it returned the status code. I have set my PayPal to IPN but am not clear about where to set the script name it will return to with completion of the credit car transaction. I am hesitant to allow someone complete access to my accounts but with itemized instructions, I can do that part.