Magic Kingdom - First week of November
Epcot - Thanksgiving Week (3rd week of November due to Food & Wine Festival)
Disney's Hollywood Studios - First or second week of November
Disney's Animal Kingdom - Second week of November
Resorts - Second or third week of November
All the Christmas festivities usually start the day after Thanksgiving and go until December 30th usually. Decorations will still be up until the 2nd week of January, sometimes pushing MLK Day Weekend.
If you have never been to Disney around the holidays, I'd say plan to deal with large crowds. If you hate crowds avoid Thanksgiving week, and December 21st through January 1st