send email notifications after administrators publish posts???

(hi I duplicated the post from http://drupal.org/node/699074 since I don't expect any reply from there. Can administrator delete/deactivate that post? thanks!)

Dear developers:

I cannot figure out how to send email notifications to post authors after administrators publish posts.
I think it is a quite common situation but I cannot find any solutions online：
user submits a post => Workflow-ng makes the post unpublished => an administrator publishes the post => (++workflow sends an email notification to the post author ++)

How to do the last step?

Thanks a lot!!!

_{Edited by WorldFallz - moved to appropriate forum.}