AJAX interaction with a Screen Reader for Section 508 users

It surely would be nice if there was some type of event or notification mechanism that an AJAX library could raise / fire / set that would cause a screen reader to notify a user that an update has occurred to part of the screen.  Perhaps this could be accomplished through some type of DOM  "event" or something similar.  Ideally, the user would like to know specifically what was updated.  I hope that everyone could get together on this and solve the problem for the screen reader / Section 508 users.

Original Post: http://morewally.com/cs/blogs/wallym/archive/2006/09/26/373.aspx