var xmlHttp = false;
try {
  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
} catch (e) {
  try {
    xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
  } catch (e2) {
    xmlHttp = false;
  }
}
if (!xmlHttp && typeof XMLHttpRequest != 'undefined') {
  xmlHttp = new XMLHttpRequest();
}

function callServer() {
  var u_name = document.getElementById("username").value;
  if ((u_name == null) || (u_name == "")) return;
  var url = "userchk.asp?username=" + escape(u_name);
  xmlHttp.open("GET", url, true);
  xmlHttp.onreadystatechange = updatePage;
  xmlHttp.send(null);  
}

function updatePage() {
  if (xmlHttp.readyState < 4) {
 userchk.innerHTML="loading...";
  }
  if (xmlHttp.readyState == 4) {
  if (xmlHttp.status == 200) {
  var response = xmlHttp.responseText;
 userchk.innerHTML=response;
  }
  }
}