unmanaged C++ - need example XML Post using certificate

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Hi,
I'm using MSXML6 in my C++ windows service app. that will be running on
Server 2003 (NOT a web server!).

I'm new to some of this, so bear with me.

I am looking for a means of posting an XML message to a web service that is
requiring a client certificate (SSL).

I have come across a few items referencing
IServerXMLHTTPRequest/ServerXMLHTTP
http://msdn2.microsoft.com/en-us/library/ms762278.aspx that seem to indicate
this is how to send the certificate.

The examples don't seem to address my issue directly.

Does someone have a "real world" example on how to do this?

Please explain such things as to where the certificate physically is
located, security considerations, etc.

Thanks.