<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Documento sin título</title>
<script language="javascript">
function obre(){
document.all['principal'].height='50%'
document.all['inferior'].height='50%';
alert("obre");
}
function maxi(){
document.all['principal'].height='0%'
document.all['inferior'].height='100%';
alert("maxi");
}
function tanca(){
document.all['principal'].height='100%'
document.all['inferior'].height='0%';
alert("tanca");
}
</script>
</head>
<body>
<iframe name="principal" id="principal" src="hoja.php" width="100%" height="400" scrolling="auto" marginheight="0" marginwidth="0" hspace="0" vspace="0" frameborder="0"></iframe>
<iframe name="inferior" id="inferior" src="inferior.php" width="100%" height="400" scrolling="auto" marginheight="0" marginwidth="0" hspace="0" vspace="0" frameborder="0"></iframe>
</body>
</html>
-- Ahora dentro de inferior.php
<input alt='Minimitzar' type='image' onClick='javascript
:parent.obre();return false;' src='images/mini.gif'> <input alt='Maximitzar' type='image' onClick='javascript
:parent.maxi();return false;' src='images/maxi.gif'> <input alt='Tancar' type='image' onClick='javascript
:parent.tanca();return false;' src='images/tancar.gif'><table width="100%" border="0" cellspacing="0" cellpadding="0">