var http = false;

if(navigator.appName == "Microsoft Internet Explorer") {
  http = new ActiveXObject("Microsoft.XMLHTTP");
} else {
  http = new XMLHttpRequest();
}

function validate(Email) {
  http.abort();
  http.open("GET", "http://www.unicasting.com/ajax/email_validate.asp?Email=" + Email, true);
  http.onreadystatechange=function() {
    if(http.readyState == 4) {
      document.getElementById('foo').innerHTML = http.responseText;
    }
  }
  http.send(null);
}