請問那一個是對的？？

In most cases, since you are likely talking about the holiday, "2006 Christmas" is correct.  In the rare circumstance when you are talking about the year 2006 instead, "2006's Christmas" can be correct.  Examples:

- The 2006 Christmas Party for all members will be held at a five-star hotel.

- The year 2006 was a memorable one for me.  In January I got a job promotion, then in the summer I met my beautiful girlfriend, and 2006's Christmas will always be remembered as when we got engaged.