function finestra(url, name, width, height) {
estilo = "resizable=0,menubar=0,toolbar=0,location=0,person a lbar=0"+
",status=0,scrollbars=1,width="+widthw+",height="+ heightw+",top="+
(screen.height-height)/2+",left="+(screen.width-width)/2;
window.open(url, name, estilo);
}
<a onclick="finestra(
http://google.com, google, 300, 350);">Ventana 1</a>
<a onclick="finestra(
http://epic.com, epic, 700, 800);">Ventana 2</a>
No lo probe por falta de ganas.
Saludos