var ventana;
function abrir_ventana(nombre,x,y) 

{
window.open(nombre,"_blank","width="+x+",height="+y+",top="+(screen.height-y)/2+",left="+(screen.width-x)/2)
}

function abrir_popup(pagina,w,h)
{	x=(screen.width-w)/2;
	y=(screen.height-h)/2;
window.open(pagina,"_blank","resizable=no,width="+w+",height="+h+",left="+x+", top="+y);
}