This screencast is part two of the introduction of tm_dialog which I did last year.

The screencast goes through:

1. A few changes made since the first screencast
2. Returning values such as list selections
3. Using the standard defaults system for keeping (UI) state across sessions
4. Asynchronous operation: not blocking TextMate and updating the dialog while on-screen

Here is a direct link to the screencast (14 minutes)