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=window.open("","new","width=500, height=500, menubar=0");
}
//-->
</script>
<form target="new" action="youdomain.com/cgi-bin/script.cgi" method="p
+ost" onSubmit="openNew()">
...
</form>
[download]

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.
jclovs