method getResponseHeader

    var request = shell.serviceManager.maxiXML.xmlHTTPRequest;
    request.open("GET","http://aol.musicnow.com/rss/genre/");
    request.onreadystatechange = function()
    {
        if(request.readyState == 4)
        {
            var contentType = request.getResponseHeader("Content-Type");
            if(contentType = "application/xml")
            {
                var XML= request.responseXML;
            }
        }
    }

    request.send("");