This extension adds a new panel to the Flash MX 2004 Authoring Tool, that enables you to specify an interval for automatically saving the document you are presently working on automatically. Intervals can be set in minutes or hours. The Auto Save panel can be found in Window > Other Panels > Auto Save.
Download the extension here or it is also attched to this thread.
To install this extension you need to have Macromedia Extension Manager 1.6 installed.