Esempio veloce
codice:
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript">	
function sndReq(action,id) {
	$("#"+id).load(action)  
}   
</script> 
</head>
<body>
<div id="div_dinamico"></div>
<div>PROVA</div>
</body>
per maggiori dettagli http://api.jquery.com/category/ajax/