Place the following code into the header of any asp document and it will redirect the page access to the correct site name while preserving the script name and the query arguments.

<%
  ' If the server name is not www.sitename.com we can do the redirect to www.sitename.com. 
  ' The only time we can is if the method is a GET
  ' (no way to pass along the POST arguments) and its on port 80 (don't want to redirect the SSL).
if ( strcomp( lcase( Request.ServerVariables("SERVER_NAME") ) , "www.sitename.com", 1 ) <> 0 _
    AND Request.ServerVariables("SERVER_PORT") = 80 _
    AND strcomp( lcase( Request.ServerVariables("REQUEST_METHOD") ) , "get" , 1 ) = 0 _
) then
    URL = "http://www.sitename.com" & Request.ServerVariables("SCRIPT_NAME")
    if len ( request.servervariables("QUERY_STRING" ) ) > 0 then
        URL = URL + "?" + request.servervariables("QUERY_STRING" )
    end if
    Response.Status="301 Moved Permanently"
    Response.AddHeader "Location", URL
    Response.End
end if
%>