It's great fun!
It runs throughout the month of October. The tickets went on sale May 1 last year.
The DIS has already posted this year's dates as being Sept 30, Oct 2, 4, 7, 11, 13, 16 18, 21, 23, 25, 27, 28, 30, 31.
The parade is great and the trick or treating is too! It's a special event at MK after park hours. They re-open from 7:00p to Midnight for ticket holders. Most of the rides are open and the lines usually aren't long unless you go Halloween night or Friday nights.
You just call Disney's main number for tickets. Watch here for when they go on sale this year.
Halloween night sells out and then the Fridays usually sell out too. Weekdays aren't as busy.