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));
if (is_nav && (is_major <= 4))
   window.open("nav4popup.htm","nav4popup","width=400,height=250,resizable=no,dependent=yes");