popups, parents, parameters, and php

I have been asking specific questions, and getting helpful answers, but I realized I am getting ahead of myself and thinking about the trees when I don't see the forest yet. I would like to describe what it is I want to do in general, and then hopefully you can point me in the right direction so I use html, php, and javascript together in some kind of reasonable way. I feel like I am re-inventing the wheel, and badly. What I want to do must have been done a zillion times by other web programmers already. I have a php page (edit.php) with a form with some text fields and a select menu (select1). I want users to be able to add entries to the select1 menu, and would like to use a popup window to do this. In the popup window, the user is presented with a form with a select menu of all possible entries. The user can make multiple selections from this list in the popup, and when the popup's form is submitted, I want the select1 menu in edit.php to reflect these additional entries selected from the popup. Those are the requirements. Should be easy, but I am finding it very difficult to tie the pieces together. Any advice or url of a relevant tutorial would be greatly appreciated. Thanks, Rich