[jQuery-Form-Validator] - Problem with rules

[niagara]

Hi guys.
This is my code:
$().ready(function() {
$("#previ").validate({
submitHandler: function() {
if(confirm('Sure?')){
$(form).submit();
return true;
}else{
return false;
}
},
rules: {
id_previsione: { required: true },
id_icona: { required: true },
id_regione: { required: $('#id_previsione').val() == 1 }, //NOTE
THIS ROWS <-----
testo_previsione: { required: true }
},
messages: {
id_previsione: { required: "is required.." },
id_icona: { required: "is required..."},
id_regione: { required: "is required..."},
testo_previsione: { required: "is required.," }
}
});
});

I don't riceve any error but it doesn't work as i expected.
I want that the rules id_regione { required: true } is applyed when
the val of id_prevision is == 1.
Understand my problem?

Many Thanks.
Best regards.