function popup( url, nom, w, h )
{
	var top =(screen.height-h)/2; 
	var left=(screen.width-w)/2;

	window.open(url, nom, "width="+w+", height="+h+", resizable=yes, scrollbars=yes, toolbar=no, location=no, directories=no, status=no, menubar=no, copyhistory=no, top=" + top + ", left=" + left);
}