Calling SOAP from ASP 3.0 or earlier - the easiest way, I believe - is to use the SoapClient object available in the MS SOAP toolkit. The toolkit can be downloaded here.
The client has 2 APIs: one is a high level API the other is a Low Level API. You can probably use the high level API which simplifies coding, assuming you have a WSDL for the Web service available. Keep in mind that when calling the MSSoapInit method from an ASP page or another multithreaded environment, you must set the ServerHTTPRequest property (using the ClientProperty property) before calling that method.
This was first published in August 2002