ASP.NET Photo Upload modal Popup window

I need help creating a modal popup window in asp.net that will freeze the parent page until the popup closes and it will refresh the parent page. The child page needs to be able to handle postbacks. I've tried creating one is javascript with showModalDialog but it won't handle postbacks. The popup window builds a dynamic associate array, a sorted list actually and the parent page needs access to that list. The parent page should be able to know when the popup is closed and react accordingly. I don't want some javascrpt code you copied from a message board, I want the exact specification shown on page 4 of the handout. I've got the code for the popup window that builds a sorted list which is the datasource for an asp listbox. I just don't know what to do when I close it to pass that list on to the parent page. I need this done ASAP! 2 days or less! Please be specific on how you will conquer this problem!