Funziona !!! Ecco come l'ho sistemato !!

codice:
<html>

	<head>
		<title>prova piani</title>
<style type="text/css">
    
      #cerchio {position : absolute; left:6px; top:8px; z-index:11}

      #rombo {position:relative; left:0px; top:0px; z-index:10}

</style>
	</head>

<body>

<div id="container">

	<span id="cerchio">[img]sopra.png[/img]</span>

	<span id="rombo">[img]sotto.jpg[/img]</span>
	
</div>
	
	
	

	</body>
</html>

Grazie !!