<script language="javascript" type="text/javascript">
function Controllo() {
if ((select1.value!="")||(select2.value!="")) {
document.form.action="...nome del form da lanciare";
document.form.submit();
return true;
}
}
</script>
</head>
<body>
<form name="form" id="form" >
<select id="select1" name="select1">
<option value="">nessuna selezione</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<select id="select2" name="select2">
<option value="">nessuna selezione</option>
<option value="1">1</option>
<option value="2">2</option>
</select>
<input type="button" value="Invia" onclick="Controllo()">
</form>
</body>
</html>