к примеру index.php:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN">
<html>
<head>
<title>New</title>
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<script type="text/javascript" src="http://code.jquery.com/jquery-1.4.2.min.js"></script>
<script type="text/javascript">//<!--
$(function(){
setInterval(
function(){
$('#m').load('some.php');
a=$('#m').html();
}
,500);
});//-->
</script>
</head>
<body>
<div style="display:none;" id="m"></div>
</body>
</html>