function ajax()
{
	var xhr = null; 
	if(window.XMLHttpRequest)
	   xhr = new XMLHttpRequest(); 
	else if(window.ActiveXObject){
	   try {
				xhr = new ActiveXObject("Msxml2.XMLHTTP");
			} catch (e) {
				xhr = new ActiveXObject("Microsoft.XMLHTTP");
			}
	}
	else {
	   alert("Votre navigateur ne supporte pas certains objets Javascript..."); 
	   xhr = false; 
	} 
	return xhr;
}