I would suggest looking at the System.Text.RegularExpression namespace and use a regular expression to do the replacement.

I messed up the links in the reply. These are the links that I meant to use. HttpWebRequest.GetRequestStream Example of the HTTP POST Offical documentation about the format of the POST body

I think you meant to point to the example in the HttpWebRequest.GetRequestStream documentation. Also an example of the HTTP POST and some of the offical documentation about the format of the POST body might help explain the Microsoft example.