Primero que nada que version de mootools usas yo para esta prueba eh usado la ultima la 1.0
Código PHP:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>prueba</title>
<script type="text/javascript" src="mootools.v1.00.js"></script>
<script language="JavaScript" type="text/javascript">
//<![CDATA[
window.addEvent('domready',function(){
var myHeight = new Fx.Slide('box1', {duration: 900});
$('height').addEvent('click',function(){
myHeight.toggle();
});
var myMargin = new Fx.Style('box4','width',{duration: 500});
$('margin').addEvent('click',function(){
myMargin.start(0, 100);
});
});
//]]>
</script>
</head>
<body>
<p><a href="javascript:void(0)" id="height">fx.Height</a></p>
<div id="box1" style="width:100px;background-color:#cccccc;"><br /><br /><br />
</div>
<p><a href="javascript:void(0)" id="margin">fx.Style</a></p>
<div id="box4" style="height:100px;width:100px;background-color:#cccccc;"> </div>
</body>
</html>
en vez de usar Fx.Height usa Fx.Slide. testeado en IE7, IE6 y FF
Estoy usando xhtml 1.0 strict solo que no em dejan poner enlaces :S