Non so se ti aiuterà....

file : test173a.html
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Untitled</title>
</head>
<body>
<script> 
 var b = window.open("test173b.html","","top=300,left=0,width=300,height=250,status=yes");
 var c = window.open("test173c.html","","top=300,left=320,width=300,height=250,status=yes");
 document.write(c.document.getElementById('h').value);
</script>
</body>
</html>

file : test173b.html
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Finestra B</title>
<script language="JavaScript" type="text/javascript">
<!--
function settC() {
 window.opener.c.document.getElementById('mydiv').innerText = document.getElementById('pippo').value;
} 
//-->
</script>

</head>
<body>
<input type="hidden" value="b" id="h">
<input type="text" id="pippo">

<input type="button" value="ok" onclick="settC()">
<div id="mydiv"></div>
</body>
</html>
file : test173c.html
codice:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

<html>
<head>
<title>Finestra C</title>
<script language="JavaScript" type="text/javascript">
<!--
function settB() {
 window.opener.b.document.getElementById('mydiv').innerText = document.getElementById('pippo').value;
} 
//-->
</script>

</head>
<body>
<input type="hidden" value="c" id="h">
<input type="text" id="pippo">

<input type="button" value="ok" onclick="settB()">
<div id="mydiv"></div>
</body>
</html>