[jQuery] [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.