secondo me la chiave dell'enigma sta qui.. il più è capire come passargli le date !!!

codice:
<script type="text/javascript">
  //
    // the default multiple dates selected, first time the calendar is instantiated
    var MA = []; 

    function closed(cal) {

      // here we'll write the output; this is only for example.  You
      // will normally fill an input field or something with the dates.
      var el = document.getElementById("output");

      // reset initial content.
      el.innerHTML = "";

      // Reset the "MA", in case one triggers the calendar again.
      // CAREFUL!  You don't want to do "MA = [];".  We need to modify
      // the value of the current array, instead of creating a new one.
      // Calendar.setup is called only once! :-)  So be careful.
      MA.length = 0;

      // walk the calendar's multiple dates selection hash
      for (var i in cal.multiple) {
        var d = cal.multiple[i];
        // sometimes the date is not actually selected, that's why we need to check.
        if (d) {
          // OK, selected.  Fill an input field.  Or something.  Just for example,
          // we will display all selected dates in the element having the id "output".
          el.innerHTML += d.print("%A, %Y %B %d") + "
";

          // and push it in the "MA", in case one triggers the calendar again.
          MA[MA.length] = d;
        }
      }
      cal.hide();
      return true;
    };

    Calendar.setup({
      align      : "BR",
      showOthers : true,
      multiple   : MA, // pass the initial or computed array of multiple dates to be initially selected 
      onClose    : closed,
      button     : "trigger"
    });
  </script>