Hi Holly,
The Extra Magic Hours are available for
Epcot and
Disney's Animal Kingdom Park for September, 2008 but not yet for Magic Kingdom or Disney's Hollywood Studios. Typically they will release the park hours including the Extra Magic Hours 6 months ahead of time, given this, I would try back between now (March 1, 2008) and the end of March periodically, I am sure these remaining 2 parks will be shown on the calendar site shortly.
As far as the hours for
"Mickey's Not-So-Scary Halloween Party", these dates have not been released yet, but if you would like an estimate, I would go by when they went on sale last year ("2007") which was May 1, 2007 and the dates of the "MNSSHP" started on September 14, 2007 until November 2, 2007 on
select evenings. I would suggest to keep trying back at the website for the release dates for this year but use last year's dates as a comparison. I hope this helps!
Best wishes,
Brigitta