Load page onclick loadXMLDoc

[miro]

Para deixar uma imagem gif, carregando para quando clicar no botão.

Quando carregado a página desaparece imagem carregando.gif.

<?php echo SHOPPING_CART_PRICE_ESTIMATE . '<br><br>' . SHOPPING_CART_POST_CODE. '<input type="text" name="postcode" id="postcode"/>' . '&nbsp;' . '<button type="button" class="myButton" onclick="loadXMLDoc(\'' . tep_href_link("shipping_quote.php") . '\')">' . ESTIMATE_BUTTON . '</button>'  ?>

<script type="text/javascript">
function loadXMLDoc(url)
{
var postcode = document.getElementById('postcode').value;
if (window.XMLHttpRequest)
  {// code for IE7+, Firefox, Chrome, Opera, Safari
  xmlhttp=new XMLHttpRequest();
  xmlhttp.onreadystatechange=stateChange;
  xmlhttp.open("GET",url+"&postcode="+postcode,true);
  xmlhttp.send(null);
  }
else
  {// code for IE6, IE5
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  xmlhttp.onreadystatechange=stateChange;
  xmlhttp.open("GET",url+"&postcode="+postcode,true);
  xmlhttp.send();
  }
}
</script>