Chris,

I believe you can access the raw SOAP by writing your own class that
inherits the SOAPExtension class.  By overriding the ProcessMessage method,
you can access the SoapMessage at each stage any stage of
serialization/deserilization.  Since you want the raw SOAP message recevied
by your Web service, you should  gear your extension to do its work at
SoapMessageStage.BeforeDeserialize.

You can check the MSDN entry for SOAPExtension for a VB.NET and C# example
of a SOAPExtension that writes the SOAP messages to a output file.

Note -- you will also need to write a SoapExtensionAttribute class so that
your webservice will have access to the SoapExtension.

Hope that helps.

Marc