Hi!
With all of the Christmas decorations up, that's a beautiful time to visit the Walt Disney World Resort.
Unfortunately, Disney has not released dates yet for Mickey's Very Merry Christmas Party for 2010. Historically, the dates are not released until late spring or early summer. However, based on when they took place the past couple of years, I would not expect he Magic Kingdom to offer the Christmas Party during your trip. The last party in 2009 was held on Friday, December 18th; the last party in 2008 was held on Friday, December 19th.
After the last party, and before the holidays end, some aspects of the party are available for all guests to experience. For example as I type this on the 1st of the year, guests visiting the Magic Kingdom can watch Mickey's Once Upon A Christmastime Parade and the Holiday Wishes fireworks show. Those are two of the biggest events held during the party.
As the year progresses, you can check
here to see if dates have been released. Enjoy planning your magical vacation and write back if you have any more questions!