var IE6 = (navigator.userAgent.indexOf("MSIE 6")>=0) ? true : false;
var IE5 = (navigator.userAgent.indexOf("MSIE 5.5")>=0) ? true : false;
if(IE6){
  alert('WARNING: This site may not function correctly using Internet Explorer 6. Please update your browser or use firefox');
}
else if(IE5){
  alert('WARNING: This site may not function correctly using Internet Explorer 5. Please update your browser or use firefox');
}