This map is covered with snow, has red nosed deers, decorated trees, and piles of gifts. Nice of them to think of this.
You can download it from here (zip file of about 10KB): Winter Wonderland Map
After you download the zip file, simply extract the Christmas.xml and Christmas.xs to your: My Documents\My Games\Age of Empires 3\RM folder (usually it should be C:\Documents and Settings\
When you host a single or multiplayer game of Age of Empires 3, check the Custom Map box in order to be able to select the Winter Wonderland map. Note that when you play multiplayer games no experience is gained when you play on Custom Maps.
Have phun playing this. And happy hollidays!