function Xhr(div, file, func)
{
	if( window.XMLHttpRequest ){
	  xhr = new XMLHttpRequest();
 
	  if ( xhr.overrideMimeType ) xhr.overrideMimeType('text/html; charset=ISO-8859-1');
	} else {
	   if ( window.ActiveXObject ){
	    try {
	      xhr = new ActiveXObject("Msxml2.XMLHTTP");
	    } catch (e) {
	      try {
	        xhr = new ActiveXObject("Microsoft.XMLHTTP");
	      } catch (e) {
	        window.alert("Votre navigateur ne prend pas en charge l'objet XMLHTTPRequest.");
	      }
	    }
	  }
	}
 
	if( (new RegExp("[?]", "gi")).test(file) ){
		xhr.open("GET", file + '&rand=' + Math.random(), true);
	} else {
		xhr.open("GET", file + '?rand=' + Math.random(), true);
	}
 
	xhr.onreadystatechange = function(){
		if(xhr.readyState == 4){
			if( div != '' ) document.getElementById(div).innerHTML = xhr.responseText;
			if( func != '' ){
				var regex = new RegExp("X", "g");
				eval(func.replace(regex, "xhr.responseText"));
			}
		}
	}
 
	xhr.setRequestHeader("Content-type", "charset=ISO-8859-1");
	xhr.send(null);
}
 
var res = '?res=1';
var width = '&width='+screen.width;
var height = '&height='+screen.height;
var params = res+width+height;
Xhr('', 'get_res.php'+params, '');