Prueba algo asi:
Código PHP:
<html>
<head>
<script LANGUAGE="JavaScript">
<!--
function pop(pag,x,y){
var propiedades = "toolbar=1, location=1, directories=1, status=1, menubar=yes, scrollbars=1, top=50, left=50, resizable=1, width="+x+", height="+y;
window.open(pag,"",propiedades);
}
//-->
</script>
</head>
<body>
<a href="#" onClick="javascript: pop('untitled-1.htm','500', '500')">abrir</a>
</body>
</html>
.
.
.
pop('paginaquequeresabrirenelpopup','ancho', 'alto')