var isNav, isIE, isMac, ie5mac, DOM5
var brVersion = parseInt(navigator.appVersion);

if (navigator.appName == "Netscape" & brVersion ==4) isNav = true;
if (navigator.appName == "Microsoft Internet Explorer" & brVersion >=4) isIE = true;
if (navigator.appName == "Netscape" & brVersion >=5) DOM5 = true;

var theAgent=navigator.userAgent
if (theAgent.indexOf("Mac") != -1) isMac = true
if (isMac && theAgent.indexOf("MSIE 5") != -1) ie5mac = true