How to Ajax auto refresh after 5 seconds

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.0/jquery.min.js"></script>
<script language="JavaScript">
setInterval( "Ajax();", 5000 );  ///////// 10 seconds
 
$(function() {
Ajax = function(){
 
$('#dataDisplay').prepend("Hi This is auto refresh example for you <br><br>").fadeIn("slow");
 
}
 });
</script>

<div id="dataDisplay" ></div>