var browser_type=navigator.appName;
var browser_version=parseInt(navigator.appVersion);
//if NS 4+
if (browser_type=="Netscape"&&browser_version>=4){

//if IE 4+
}else{
if (browser_type=="Microsoft Internet Explorer"&&browser_version>=4){

//Default goto page (NOT NS and NOT IE)
}else{
window.location="upgrade.html";
}
}