Hay un pequeño detalle que olvidé añadir...
Código:
<html>
<head>
<script languaje="JavaScript">
var nPop = 0;
function nuevaVentana(){
var oPop = window.open();
oPop.document.open();
oPop.document.write("<html>");
oPop.document.write("<head>");
oPop.document.write("</head>");
oPop.document.write("<body onload='javascript:window.moveTo(" + nPop + "," + nPop + "); window.resizeTo(100, 100)'>");
oPop.document.write("</body>");
oPop.document.write("</html>");
oPop.document.close();
nPop += 50;
}
</script>
</head>
<body>
<form name="formulario">
<input type="button" name="boton" onclick="nuevaVentana()" value="Nuevo PopUp">
</form>
</body>
</html>
Saludos.