// threadsafe asynchronous XMLHTTPRequest
function ajaxSend(url, callback)
{

  // we use a javascript feature here called "inner functions"
  // using these means the local variables retain their values after the outer function
  // has returned. this is useful for thread safety, so 
  // reassigning the onreadystatechange function doesn't stomp over earlier requests.


  function ajaxBindCallback()
  {
    if (ajaxRequest.readyState == 4) 
	  {
      if (ajaxRequest.status == 200) 
		  {
        if (ajaxCallback)
			  {
          ajaxCallback(ajaxRequest.responseText);
        } 
			  else 
			  {
          alert('no callback defined');
        }
      } 
		  else 
		  {
        alert("error: "+ajaxRequest.status+" - "+ajaxRequest.statusText );
      }
    }
		else
		{
		  ajaxCallback("Searching...");
		}
  }


  // use a local variable to hold our request and callback until the inner function is called...
  var ajaxRequest = null;
  var ajaxCallback = callback;
 

  // bind our callback then hit the server...
  if (window.XMLHttpRequest) 
  {
    // moz et al
    ajaxRequest = new XMLHttpRequest();
    ajaxRequest.onreadystatechange = ajaxBindCallback;
    ajaxRequest.open("GET", url, true);
    ajaxRequest.send(null);

  } 
  else
    if (window.ActiveXObject) 
	{ 
	  {
      // ie
      ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
      if (ajaxRequest) 
		  {
        ajaxRequest.onreadystatechange = ajaxBindCallback;
        ajaxRequest.open("GET", url, true);
				ajaxRequest.setRequestHeader("If-Modified-Since", "Sat, 1 Jan 2000 00:00:00 GMT");
        ajaxRequest.send();

      }
    }
  }
}