function ajax_requete_init()
    {
    var httpRequest = false;
    if (window.XMLHttpRequest) { // Mozilla, Safari,...
        httpRequest = new XMLHttpRequest();
        if (httpRequest.overrideMimeType) {
            httpRequest.overrideMimeType('text/xml');
            }
        }
    else if (window.ActiveXObject) { // IE
        try {
            httpRequest = new ActiveXObject("Msxml2.XMLHTTP");
            }
        catch (e) {
            try {
                httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
                }
            catch (e) {}
            }
        }

    if (!httpRequest) {
        alert('Impossible de créer une instance XMLHTTP!');
        return false;
        }
    return httpRequest;
    }

function ifr_ecrire(id,src,larg,haut)
	{
	document.getElementById(id).innerHTML='<iframe width="'+larg+'" height="'+haut+'" src="'+src+'" marginwidth="0"  marginheight="0" scrolling="no" frameborder="0"></iframe>';
	}