How can I pass information between dialogs?

I have a plugin that I made for FCKeditor. It displays a dialog and gives the user some options. One of such options opens another dialog (Ill call this the "popup"). Here's a picture:

FCKEditor => plugin window => popup =>

How can I make it so when a user clicks okay in the popup window, information is sent back to the dialog (the main plugin window)?

Is this possible using javascript? Perhaps Ajax?

Thanks