<script type='text/javascript' src='script/js/calendar.js'></script>
<script type='text/javascript' src='script/js/calendar-es.js'></script>
<script type='text/javascript' src='script/js/calendar-setup.js'></script>
y dentro de tu funcion de ajax en la hoja padre pones el codigo del calendar.setup.
ejemplo: (yo cambie los campos del calendar.setup)
<script>
function loadXMLDoc(url,cfunc){if(window.XMLHttpRequest)xml http=new XMLHttpRequest;else xmlhttp=new ActiveXObject('Microsoft.XMLHTTP');xmlhttp.onready statechange=cfunc;xmlhttp.open('GET',url,true);xml http.send()}
Nombre_funcion(str){loadXMLDoc('Pagina_a_cargar.ph p?q='+str,function(){if(xmlhttp.readyState==4&&xml http.status==200){document.getElementById('Div_a_c argar').innerHTML=xmlhttp.responseText;Calendar.se tup({
inputField: 'fecha1',
ifFormat: '%d/%m/%Y',
weekNumbers: false,
displayArea: 'fecha_usuario',
daFormat: '%d/%m/%Y'
});}else{document.getElementById('Div_a_cargar').i nnerHTML='<img src=../img/ajax_loading.gif id=load_img /> ';}});} </script>