I have 2 popup windows... a main one and a child of the main...

I need to write from the main window to the child.. this is part of a desktop application, so here we go:

Main File: director.html

Code:
<html>
<head>
<SCRIPT TYPE="text/javascript">
<!--//
function installWindow1()
{
    netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserWrite");
    window.menubar.visible     = false;
    window.directories.visible = false;
    window.statusbar.visible   = false;
    window.toolbar.visible     = false;
    window.locationbar.visible = false;
    window.personalbar.visible = false;
    window.scrollbars.visible  = true;
    //window.fullscreen	       = true;
    window.outerWidth          = 840;
    window.outerHeight         = 630;
    window.screenY             = 0;
    window.screenX             = 0;
    //window.innerHeight         = 610;
    //window.innerWidth          = 810;
    netscape.security.PrivilegeManager.disablePrivilege("UniversalBrowserWrite");
    location.href = 'http://localhost/cvideo/director/home.php';
}
function installWindow2()
{
	day    = new Date();
	id     = day.getTime();
	w4     = window.open( 'till.html', id, 'toolbar=0,scrollbars=1,location=0,statusbar=0,menubar=0,resizable=0,width=10,height=10');
}
function install_window()
{
    installWindow1();
    installWindow2();
}
//-->
</script>
</head>
<body onload="install_window();">
</body>
</html>
Child File (Launched from code above) till.html

Code:
<html>
<head>
<SCRIPT TYPE="text/javascript">
<!--//
function install_window()
{
    netscape.security.PrivilegeManager.enablePrivilege("UniversalBrowserWrite");
    window.menubar.visible     = false;
    window.directories.visible = false;
    window.statusbar.visible   = false;
    window.toolbar.visible     = false;
    window.locationbar.visible = false;
    window.personalbar.visible = false;
    window.scrollbars.visible  = true;
//  window.fullscreen	       = true;
    window.outerWidth          = 840;
    window.outerHeight         = 460;
    window.screenY             = 300;
    window.screenX             = 185;
    //window.innerHeight         = 610;
    //window.innerWidth          = 810;
    netscape.security.PrivilegeManager.disablePrivilege("UniversalBrowserWrite");
    location.href = 'http://localhost/cvideo/director/till.php';
}
//-->
</script>
</head>
<body onload="install_window();">
</body>
</html>
How would I do it? i tried w4.document...... but it says w4 is undefined..

-Eric