function popup(url,titre,W,H){
	if (document.layers){
		var xMax = window.outerWidth
		var yMax = window.outerHeight;
	}else{
		var xMax = screen.width;
		var yMax = screen.height;
	}
	var xOffset = (xMax - W)/2;
	var yOffset = (yMax - H)/2;
	ff=window.open(url, titre, "width="+W+", height="+H+", resizable=no, scrollbars=yes, status=no, screenX=" + xOffset + ", screenY=" + yOffset + ", top=" + yOffset + ", left=" + xOffset + "");
	ff.focus();
}