denedim sorun yok.
<html>
<head>
<script type="text/javascript">
function yukle()
{
setTimeout("degistir()",10000);
}
function degistir()
{
document.getElementById("arama").src= "http://google.com";
}
</script>
</head>
<body onLoad="yukle()">
<iframe src="http://www.bing.com/" width="660" height="660" marginwidth="0" marginheight="0" border="0" id="arama" frameborder="0" borders="0"></iframe>
</body>
</html>