NS4 = (document.layers) ? true : false;
IE4 = (navigator.appVersion.indexOf("MSIE 4.")==-1)? false : true;
IE5 = (navigator.appVersion.indexOf("MSIE 5.")==-1) ? false : true;
IE6 = (navigator.appVersion.indexOf("MSIE 6.")==-1) ? false : true;
IE7 = (navigator.appVersion.indexOf("MSIE 7.")==-1) ? false : true;

if(NS4 || IE4 || IE5 || IE6){
	alert('please upgrade your web browser!');
}

if(IE7){
    alert('You will may not see this page as expected, please upgrade your web browser!');

}