function getXmlHttpRequestObject() {
 if (window.XMLHttpRequest) {
    return new XMLHttpRequest(); 
 } else if (window.ActiveXObject) {
    return new ActiveXObject("Microsoft.XMLHTTP"); 
 } else {
    
    alert("Your browser doesn't support the XmlHttpRequest object.");
 }
}
var Req = getXmlHttpRequestObject();

function makeRequest(url, param) {

 if (Req.readyState == 4 || Req.readyState == 0) {
  
   Req.open("POST", url, true);
   
   Req.onreadystatechange = updatePage; 

  
   Req.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
   Req.setRequestHeader("Content-length", param.length);
   Req.setRequestHeader("Connection", "close");

  
   Req.send(param);
 }   
}

function updatePage() {

 if (Req.readyState == 4) {
  
   img = document.getElementById('imgCaptcha'); 
  
   img.src = 'create.php?' + Math.random();
 }
}

function getParam(theForm) {

 var url = 'mail.php';
 
 var postStr = theForm.txtCaptcha.name + "=" + encodeURIComponent( theForm.txtCaptcha.value );
 
 makeRequest(url, postStr);
}