C# .NET httpwebrequest/response in XMLDocument format

Hello, I need to have a simple purchase of one item processed via Desjardins Bank in Canada as per documentation: [login to view URL] Thank you, All i need is a html page with a 'buy' button (no design), Item1-price$10, GST,PST,TOTAL subimtted and processed by the Desjardins Payment Systems (with redirection). It's a sandbox so only the xml responses are meningful. There are 7 steps of simple XML communication back and forth until the transaction is posted. Basically i need working HTTPWebRequests sending XML and receiving an XML response (XMLDocument format). Please note that this is a .NET C# project.