How can I add loading image into this script?

var xmlhttp;

function showUser(str)
{
xmlhttp=GetXmlHttpObject();
if (xmlhttp==null)
  {
  alert ("Browser does not support HTTP Request");
  return;
  }
var url="cars.php";
url=url+"?q="+str;
url=url+"&sid="+Math.random();
xmlhttp.onreadystatechange=stateChanged;
xmlhttp.open("GET",url,true);
xmlhttp.send(null);
}

function stateChanged()
{
if (xmlhttp.readyState==4)
  {
  xmlDoc=xmlhttp.responseXML;
  document.getElementById("name").innerHTML=
  xmlDoc.getElementsByTagName("name")[0].childNodes[0].nodeValue;
  document.getElementById("description").innerHTML=
  xmlDoc.getElementsByTagName("description")[0].childNodes[0].nodeValue;
  }
}

function GetXmlHttpObject()
{
if (window.XMLHttpRequest)
  {
  // code for IE7+, Firefox, Chrome, Opera, Safari
  return new XMLHttpRequest();
  }
if (window.ActiveXObject)
  {
  // code for IE6, IE5
  return new ActiveXObject("Microsoft.XMLHTTP");
  }
return null;
}

ad and else statement in your state changed function where ready state =4. you can add your image until the document is ready to show what its retrieving from the server.

I am really far from this code.
I found this script on w3.org