function clearText(field){ 
    if (field.defaultValue == field.value) field.value = '';
    else if (field.value == '') field.value = field.defaultValue;
}

function submit_ajax(form, id) {
    action = $(form).attr('action');
    $.ajax({
        type: 'POST',
        url: action,
        data: $(form).serialize(),
        success: function(data) {
            $(id).html(data);
        }
    });

    return false;
}