Hi Susan,
It's lovely to receive a question from a fellow Brit!
Firstly,
Mickey's Not-So-Scary Halloween Party which is held on select nights from 11 September - 2 November 2012 at the Magic Kingdom Theme Park is a lot of fun! It includes Mickey's "Boo-to-You" Halloween Parade, Happy HalloWishes fireworks extravaganza and many of the Disney characters and villains in special halloween costumes. Not to mention trick-or-treating throughout the Magic Kingdom theme park which is my Sons absolute favourite thing to do whilst visiting Walt Disney World at this time of year.
Haunted Carriage Rides through the woods of Disney's Fort Wilderness Resort where Guests can experience chilling sights and sounds inspired by the Legend of Sleepy Hollow have been available in previous years although no official announcement has been made about whether these will be offered this year as of yet. For pricing and availability, I would recommend calling (407) WDW-PLAY or (407) 939-7529 nearer the time.
Also, in previous years, most Disney Resort hotels have offered a variety of Halloween activities on Halloween itself such as pumpkin decorating or Halloween Monster Mash parties. You'll want to check the calendar of events for your Resort hotel when you arrive to see what activities (if any) will take place this year.
I hope that this information has been of help and wish you a spooktacular trip!