Hi Roberto! The fall season is a wonderful time of year to visit Walt Disney World! Not only is the weather beautiful, but the crowds are light and, just as you mentioned, you might be able to see both Halloween and Christmas decorations!
While the decorations schedule varies year-by-year and cannot be guaranteed, Halloween decorations typically begin to appear around August and are usually taken down after the last Mickey's Not-So-Scary-Halloween Party, which was on November 1 in 2011.
The Christmas decorations are always on display by the first Mickey's Very Merry Christmas Party, which was on November 8 in 2011.
Your best bet for enjoying both the Halloween and Christmas decorations is to visit the first week in November. If you plan a vacation for that week, plan to buy tickets for both the Mickey's Not-So-Scary Halloween Party and the Mickey's Very Merry Christmas Party. I've been to both of the parties and they are a blast! Check out the
Walt Disney World Special Events page for more information on these fun events!
I hope you have a magical vacation!
Magically,
Stacy