var agt=navigator.userAgent.toLowerCase(); 
var is_mac = (agt.indexOf("mac")!=-1); 
var version = parseInt(navigator.appVersion); 
var is_ie = (agt.indexOf("msie")!= -1); 
var is_ie5 = (is_ie && (version = 5));
if (is_mac && is_ie5) {location.replace("update.html")}