Vi ringrazio per i suggerimenti ma continua a non funzionare,
per chiarezza posto l'intero codice:

codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>test</title>
<style type="text/css"> 
body { 
text-align: center; 
} 
.C_Layer_3 { 
margin: 0px auto 0px auto; 
position:absolute; 
z-index:3; 
} 
</style> 


<script language="JavaScript" type="text/JavaScript">
function MM_reloadPage(init) {
if (init==true) with (navigator) {
	if ((appName=="Netscape")&&(parseInt(appVersion)==4)) {
		document.MM_pgW=innerWidth; document.MM_pgH=innerHeight; onresize=MM_reloadPage;
	}
}
else if (innerWidth!=document.MM_pgW || innerHeight!=document.MM_pgH) location.reload();
}
MM_reloadPage(true);
</script>

<script language="JavaScript" type="text/javascript">
var readyToResize=false;
function rW(){
	return (window.innerWidth)?window.innerWidth:
		   (document.documentElement.clientWidth)?document.documentElement.clientWidth:
		   (document.body.clientWidth)?document.body.clientWidth:0;
}
function rH(){
	return (window.innerHeight)?window.innerHeight:
		   (document.documentElement.clientHeight)?document.documentElement.clientHeight:
		   (document.body.clientHeight)?document.body.clientHeight:0;	
}
function riposiziona(){ 
	var el=document.getElementById('Layer2') 
	el.style.top=(rH()-265)+'px'; 
	el.style.left=(rW()-340)+'px'; 
	el.style.visibility='visible'; 
	readyToResize=true; 
}
window.onresize=function(){
	if(readyToResize){
		riposiziona();
	}
}
</script>

</head>
<body>
	<div id="Layer1" style="position:absolute; width:340px; height:265px; z-index:1; left: 0px; top: 0px;">[img]img/fondo_l_t.jpg[/img]</div>
	<div id="Layer2" style="position:absolute; width:340px; height:265px; z-index:2; left: 0px; top: 0px;">[img]img/fondo_r_d.jpg[/img]</div>
	<div id="Layer3" class="C_Layer_3">[img]img/my_logo.jpg[/img]</div>
	<script type="text/javascript">riposiziona()</script> 
</body>
</html>
per le img del (Layer1 e Layer2) Link
Sono compresse in 7-zip (http://www.7-zip.org/it/)
per il logo (Layer3) Logo per il test (uno vale l'altro)

cichity74