in reply to Opening a sizeable window with a

Okay, in short no. Not without JavaScript. I'm sorry but that is the only path of which you can follow, unless my experience treats me wrong.
So, try this in you form:
<script> <!-- function openNew() {"","new","width=500, height=500, menubar=0"); } //--> </script> <form target="new" action="" method="p +ost" onSubmit="openNew()"> ... </form>

P.S. if they don't have JavaScript support there is no reason to consider being able to do such an activity to their window.