codice:
<html>
<head>
<title></title>
<script language="javascript">
<!--
function campo(opz,nome){
div = document.getElementById('divTesto')
if(opz=='mar'||opz=='gio'||opz=='ven')
{
div.innerHTML='<select name="menu2"><option>non selez</option><option selected>selez</option></select>';
alert('pianeta: '+nome)
}
else
{div.innerHTML='' }
}
//-->
</script>
<body>
<form name="myForm">
</form>
<select name="menu1" onchange="campo(this.options[this.selectedIndex].value,this.options[this.selectedIndex].text)">
<option value='sel'>Seleziona un'opzione</option>
<option value='mar'>marte</option>
<option value='gio'>giove</option>
<option value='ven'>venere</option>
</select>
<div id="divTesto"></div>
</body>
</form>
ciao