Jquery :: Validate Textbox On Option Selected Value

I have this validate code to validate a textbox if the user select a combo value:
<script type="text/javascript">
$(document).ready(function() {
$("form#2form").validate({
rules: {
viaAltro: {
required: "#AltraVia:checked"
}},
messages: {
viaAltro: {
required: "Insert 'Altra via'"
}}})});
</script>
and this is the HTML:
<select name="viaFornitura" id="viaFornitura">
<option>Seleziona la via</option>
<option id="AltraVia">Altro</option>
</select>
<label for="viaAltro">Altra via</label>
<input name="viaAltro" id="viaFornituraAltro" type="text" />
but it doesn't work.