Download and unzip "Lingo.tmbundle.zip", and then double-click "Lingo.tmbundle" and 
confirm that you want to install it in TextMate.

The Lingo bundle supports:
- Function list
- fold/unfold functions and block structures
- comment/uncomment current selection with Command+/

It also comes with a theme called "Lingo" that mimics Director's default syntax colors.
(You might have to restart TextMate before the theme is available).