I'm assuming that what you want is to post the form to a new window? (since your example code for window.open refers to the same page that the form posts to.)
If this is the case you can just add a target="_blank" attribute to the <form> tag.
In general, if you want to do some
js before the form submits, you can either:
1. use the onsubmit event of the form
2. change the submit button to a regular html button which runs your
js and then calls formname.submit()
hth
Phil