var agt=navigator.userAgent.toLowerCase();
var is_major = parseInt(navigator.appVersion);

var is_nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
                && (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
                && (agt.indexOf('webtv')==-1) && (agt.indexOf('hotjava')==-1));

var is_nav4 = (is_nav && (is_major == 4));

if (is_nav4)
window.alert("This application requires Internet Explore 5.0 and above. Please update your browser.")