How to catch datepicker events ?

How to catch datepicker events ?

Hi to all !!! :D... I am really excited as I have discovered this
javascript library !!! :D... Just wanted to know how to catch
datepicker events ? such as when the user selects a different date...
this is my idea... that according to the selected day, month and year
I get through ajax the information about my friend's birthday...
I saw there is this code...
  <script type="text/javascript">

            //define function to be executed on document ready
            $(function(){

                //define config object for localisation
                var frenchOpts = {
                    clearText: "Limpiar",
                    closeText: "Cerrar",
                    currentText: "Courant",
                    dayNamesMin: [ "Domingo", "Lunes", "Martes", "Miercoles", "Jueves", "Viernes", "Sábado" ],
                    firstDay: 1,
                    monthNames: [ "Enero", "Febrero", "Marzo", "Abril", "Mayo", "Junio", "Julio", "Agosto", "Septiembre", "Octubre", "Noviembre", "Diciembre" ],
                    nextText: "Proximo",
                    prevText: "Previo"
                };

                //create the date picker
                $("#date").datepicker(frenchOpts);
                $("#date").datepicker({
   onChangeMonthYear: function(year, month, inst)
   {

   }
});
            });
        </script>
Sorry if someone sees something really wrong... I am trying to learn as this is something really new for me... I love Java but web developing is blowing up my mind...

Could someone post a complete example of this... or where I should put
this code in order to do this ?. It's will be easier as I know
something about php and ajax...
Thankx in advanced... I should be goinmg as I am going to a camp
today... Bye Bye