var ie4 = ns4 = ns6 = false;
var is_major = parseInt(navigator.appVersion);
if(navigator.appName == "Microsoft Internet Explorer" && parseInt(navigator.appVersion) >= 4) { ie4 = true; }
else if(navigator.appName == "Netscape" && is_major >= 4 &&  is_major < 5)  { ns4 = true; ie4 = false; }
else if(navigator.appName == "Netscape" && is_major >= 5) { ns6 = true; ie4 = ns4= false; }