Togli l'istanza dalla function.ready (meglio non riesco a spiegartelo) e richiami il datepicker da funzione:
codice:
function date_Picker(){
$("#from").datepicker({
  showOn: "button",
  buttonImage: "http://jqueryui.com/resources/demos/datepicker/images/calendar.gif",
  buttonImageOnly: true,
  buttonText: "Select date",
  defaultDate: "+1w",
  changeMonth: true,
  changeYear: true,
  numberOfMonths: 1,
  onClose: function(selectedDate) {
    $("#to").datepicker("option", "minDate", selectedDate);
  }
});


$("#to").datepicker({
  showOn: "button",
  buttonImage: "http://jqueryui.com/resources/demos/datepicker/images/calendar.gif ",
  buttonImageOnly: true,
  buttonText: "Select date",
  defaultDate: "+1w",
  changeMonth: true,
  changeYear: true,
  numberOfMonths: 1,
  onClose: function(selectedDate) {
    $("#from").datepicker("option", "maxDate", selectedDate);
  }
});
}