The ASP Server Variables collection (Request.ServerVariables) is used to retrieve server variable values... these variables include information about the server where the script is executed AND (more importantly) all of the HTTP header infromation that is sent by the client's browser.  To familiarize yourself with all of the available server variables, save the attached variables.zip to your PC and extract it... then upload the extracted variables.asp to your site, and visit http://www.yourdomain.com/variables.asp and review the wealth of information available from this collection: