Yes, go to System Preferences > Desktop and Screen Saver.
on the left there`s a plus sign, that means that you can choose a folder, you choose the folder where all your Christmas photos are, then you`ll see your christmas photos thumbnails, check the option to change the wallpaper every X minutes! and there you go!
Well, that`s the way on SL
Thanks, that works. I should have switched to a mac a long time ago.