This version of the web client for the contacts samples is based around some Microsoft only technology - XMLHTTP. This technology is useful as a sample because it provides the clearest view of how the documents flow from the browser and back again.
Lets start with a request or submission. View the source html for the add a company page. This is a simple html form except for the way that the data is sent back to the server. There is an XML template document with the web page and when the submit button is clicked the template is loaded and nodes are created using the values in the input fields and then the resulting XML document is sent to the server using XMLHTTP. At this point there are 2 ASP scripts that handle what happens next. The first one receives the XML document and then sends it to ComponentX (process.asp). This is the process of submission and everything is done with XML.
To get the reply there is a second ASP script (process2.asp) that sets the appropriate encoding type and send the resultant XML back to the browser. If you view the source of one the pages that is returned after a form submission you will see that what the browser received was an XML document.
The entire process used XML from submission, through all processing and for returning the result to the browser.