Hi Susan,
So awesome to see you are already planning for 2012!
This year the Disney Parks Blog announced the 2011
Mickey's Not-So-Scary Halloween Party (MNSSHP) dates on May 2, 2011. One would guess (I don't know for sure) that the 2012 dates will be announced around that time next year as well.
Near the end of April 2012, I'd recommend to start keeping your eyes on the
Disney Parks Blog. They usually make announcements there. If you're on twitter, follow @DisneyParks & @WaltDisneyWorld. If you're on Facebook, keep an eye on the official
Disney World Facebook page. You're also welcome to check back with us around that time.
MNSSHP does require a separate special event ticket to attend & only those Guests with the special event tickets are allowed to enter or remain in the park when the party begins. Guests who want to spend the day at the Magic Kingdom (MK) & attend MNSSHP on the same day will need 2 different tickets - a regular ticket for admission during the day (MK closes at 7:00 p.m. on MNSSHP dates) & a ticket to MNSSHP for that evening.
MNSSHP begins at 7:00 p.m. & lasts until midnight. Once party goers enter the park, they are given a special wrist band which indicates they have tickets to this event. Cast Members will be stationed at the entrances to the different themed lands. Guests who aren't wearing wrist bands for the event that evening will be asked to make their way down Main Street to exit the park.
If you decide that you are going to do both, I'd concentrate on the rides and attractions during the day and focus on the special events that only occur during MNSSHP. It really is awesome fun!
Wishing you many magical memories :-) Allison