Hi,
If you are using this for the IPN, you only need to "URL decode" the values passed to you by the IPN through the post. the term URL decode does not mean that you actually have to get the URL, it is just a form of encoding in order to insure that the values are passed correctly to your server.
Here is an example of a form valriable that you would need to decode
string ap_CustFirstName = HttpUtility.UrlDecode(Request.Form["ap_custfirstname"]);
Regards,
Ali