The second field that just says 'popup' is the object name for the new page. Name it safely as if you were naming a variable or it will cause problems.
Also, once you get a page open, you can use this code at the beginning (but inside the body, not the head) to make it resize/reposition:
I used screen.avail.Width,screen.availHeight to show you how to make it a full-screen window (more or less), but you can use numbers instead like 640,480 or you can use math like screen.avail.Width/2,screen.availHeight/2 to get sizes in proportion to the user's screen.