var x = screen.width;
var y = screen.height;
function abrir_ventana(ancho,alto, mipagina){
	window.open(mipagina, "", "height="+alto+",width="+ancho+", left="+(x-ancho)/2+", top="+(y-alto)/2 +", scrollbars=yes , status=no, titlebar = yes");
	}