function openAjax()
{
var xhr = null;
	if(window.XMLHttpRequest) {
		xhr = new XMLHttpRequest();
	} else if(window.ActiveXObject) {
		try {
			xhr = new ActiveXObject('Msxml2.XMLHTTP');
		} catch(e) {
			try {
				xhr = new ActiveXObject('Microsoft.XMLHTTP');
			} catch(e) {}
		}
	}
	return xhr;
}
function ajaxGetData(_url)
{
var xhr = openAjax();

	if(!xhr) {
		alert('Erreur de communication avec le serveur');
		return null;
	}

	xhr.open('GET', _url, false);
	xhr.send();
	if(xhr.status!=200) {
		return null;
	}
	return xhr.responseText;
}