Prova così
Codice PHP:
<select name="regioni" id="regioni" onChange="loadList('province', getSelected(this)); loadList('comuni', getSelected(document.getElementById('provincie')));" >
</select></td>
</tr>
<tr>
<td><label for="regioni">Provincia</label></td>
<td><select name="province" id="province" onChange="loadList('comuni', getSelected(this));">
</select> </td>
</tr>
<tr>
<td><label for="regioni">Comune</label></td>
<td><select name="comuni" id="comuni">
</select>