jQuery.validator.addMethod("require_from_group", function(value, element, options) {
    numberRequired = options[0];
    selector = options[1];
    //Look for our selector within the parent form
    var validOrNot = $(selector, element.form).filter(function() {
         // Each field is kept if it has a value
         return $(this).val();
         // Set to true if there are enough, else to false
      }).length >= numberRequired;

    //The elegent part - this element needs to check the others that match the
    //selector, but we don't want to set off a feedback loop where all the
    //elements check all the others which check all the others which
    //check all the others...
    //So instead we
    //  1) Flag all matching elements as 'currently being validated'
    //  using jQuery's .data()
    //  2) Re-run validation on each of them. Since the others are now
    //     flagged as being in the process, they will skip this section,
    //     and therefore won't turn around and validate everything else
    //  3) Once that's done, we remove the 'currently being validated' flag
    //     from all the elements
    if(!$(element).data('being_validated')) {
    var fields = $(selector, element.form);
    //.valid() means "validate using all applicable rules" (which 
    //includes this one)
    fields.data('being_validated', true).valid();
    fields.data('being_validated', false);
    }
    return validOrNot;
    // {0} below is the 0th item in the options field
}, jQuery.format("Compila almeno {0} campo."));


// "filone" is the class we will use for the input elements at this example
jQuery.validator.addClassRules("fillone", {
    require_from_group: [1,".fillone"]
});

//"filone_due" is the class we will use for the input elements at this example
jQuery.validator.addClassRules("filone_due", {
    require_from_group: [1,".filone_due"]
});