insomma sono proprio le basi

<form name="myform" action="myscript.php" method="post">

<select name="quellochemipare" onchange="this.form.submit()" >

<option value="00">00</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>


</select>

</form>