File xmlhttp.js
var xmlhttp = false ;


if (!xmlhttp && typeof XMLHttpRequest != ‘undefined’)
{
try {
xmlhttp = new XMLHttpRequest ();
}
catch (e) {
xmlhttp = false}
}


function myXMLHttpRequest ()
{
var xmlhttplocal;
try {
xmlhttplocal = new ActiveXObject (”Msxml2.XMLHTTP”)}
catch (e) {
try {
xmlhttplocal = new ActiveXObject (”Microsoft.XMLHTTP”)}
catch (E) {
xmlhttplocal = false;
}
}

if (!xmlhttplocal && typeof XMLHttpRequest != ‘undefined’) {
try {
var xmlhttplocal = new XMLHttpRequest ();
}
catch (e) {
var xmlhttplocal = false;
}
}
return (xmlhttplocal);
}

var mnmxmlhttp = Array ();
var mnmString = Array ();
var mnmPrevColor = Array ();
var responsestring = Array ();
var myxmlhttp = Array ();
var responseString = new String;

var i=0;
var ii = 0;
function ajax_update()
{
url = “ajax_php.php”;
target2 = document.getElementById (’content’);
ii = i++;

var content = “i=” + ii ;

mnmxmlhttp = new myXMLHttpRequest ();
if (mnmxmlhttp) {
mnmxmlhttp.open (”POST”, url, true);
mnmxmlhttp.setRequestHeader (’Content-Type’,
‘application/x-www-form-urlencoded’);

mnmxmlhttp.send (content);
errormatch = new RegExp (”^ERROR:”);

target2 = document.getElementById (’content’);

mnmxmlhttp.onreadystatechange = function () {
if (mnmxmlhttp.readyState == 4) {
mnmString = mnmxmlhttp.responseText;

if (mnmString.match (errormatch)) {
mnmString = mnmString.substring (6, mnmString.length);

target = document.getElementById (’content’);
target2.innerHTML = mnmString;

} else {
target = document.getElementById (’content’);
target2.innerHTML = mnmString;

}
}
}
}
setTimeout(’ajax_update()’, 20000);
}

File ajax_php.php

<?PHP
echo “<PRE>”;
print_r($_POST);
echo time();
?>

File test.html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>PHP + Ajax auto refresh DIV</title>
<script language="JavaScript" type="text/javascript" src="xmlhttp.js"></script>
</head>
<body onload="ajax_update();">
<divid="content">Loading....</div>
</body>
</html>

I tested these three scripts more than 10 times, it's works.
please just replace the ' “  ' with '  "  '

Or download the script here.ajax auto refresh script download