guarda se così ti va

codice:
<html> 

<head>

<SCRIPT LANGUAGE="JavaScript">
var source;

function change(pop)
{
	source = pop + ".html";
	document.getElementById('FX').src = source;
}

</SCRIPT>

</head>

<body>

<a href="#ese" onclick ="change('medium');">
   <img src = "opg/wast.gif">

</a>

<iframe name="FX" id="FX" width="200" height="200" src="long.html" scrolling="auto">
</iframe>

</body>

</html>