[Aetae]

$(document).ready(function() {
    $('select[id^="select_"]').change(function() {   
 
        var currentId = this.id.replace('select_', ''), 
            selectId = $('#select_' + currentId + ' :selected').val();
 
        $.ajax({
 
            type: "POST",
            url: "ajax.php",
            data: "id=" + selectId,
            dataType: 'json',
            success: function(data) {
 
                var obj = $.parseJSON(data);     
 
                $.each(data, function(i, item) {
                    var id = (data[i].id);
                    var name = (data[i].name);
 
                    $("#result_0_" + currentId).val(id + $('#result_0_' + currentId).val().replace("placeholder", data));
                    $("#result_1_" + currentId).val(name + $('#result_1_' + currentId).val().replace("placeholder", data));
 
                });
            }
        });
    });
});

P.S. Гадость эта ваша Jquery. =\