var AJAXForms = false;
var LastField = null;
var isIE = false;
// on !IE we only have to initialize it once
if (window.XMLHttpRequest) {
	AJAXForms = new XMLHttpRequest();
}

function CheckField(field) {

  if(window.XMLHttpRequest) 
     {
       // Gecko (Firefox, Moz), KHTML (Konqueror, Safari), Opera, Internet Explorer 7
      AJAXForms = new XMLHttpRequest(); 
       } 
       else if(window.ActiveXObject) 
       {
        try
        {
        // Internet Explorer 6 
        AJAXForms = new ActiveXObject("MSXML2.XMLHTTP"); 
        } 
		        catch(e) 
		        {
			        // Internet Explorer 4,5 
			        AJAXForms = new ActiveXObject("Microsoft.XMLHTTP"); 
		        }
		        } 
	        else 
	        {
		        alert("Non è possibile creare l'oggetto che fa la richiesta http");
		        return;
	        }
  AJAXForms.onreadystatechange = processChange;
  AJAXForms.open("GET", "check_form.php?op=ajax&field=" +field.name+"&value=" + field.value);

  LastField = field.name;
  AJAXForms.send(null);
}
function processChange() {
  if (AJAXForms.readyState == 4) {
var  res = document.getElementById(LastField+"check");
    res.innerHTML = AJAXForms.responseText;
    res.style.visibility = "visible";   
  }
}
//response.write(AJAXForms);