Soliciting opinions on the best way to implement

I'm developing a (seemingly) simple Web application for a customer. The application consists of two pages: a Main aspx page and a Popup aspx page. I'm building the static portions of both pages in markup, and the dynamic values I'm filling in at run time (C#).
The problem is the interaction with the popup page. By using the AJAX Control Toolkit's Modal Popup Extender, I cobbled together the popup page that displays when the user clicks a button on the main page. The popup page displays (with an error under IE, but not under Chrome), and I dynamically create a Table on the popup page. It has "n" rows, but a known number of columns. The first cell of each row holds a radio button. When the radio button is clicked I want to capture that row's information. They might click another button, in which case I'd overwrite the first information with the new information. In any case, they have to click a Close button to dismiss the popup window and pass whatever inform ...