As for today (2nd half of March, 2012), the Creation Kit does not have an option which allows to add new idle animations/poses to the game in any way. There are some work-around methods, but one of easiest ways to add new idle animations/poses to the game is by using Fore's modified behavior files and esm file of Director's Tools mod as a base.
This tutorial focuses on the process of adding new idle animations and poses for default characters (races), it doesn't cover creature or object animations.
For animators (persons who create animations) this tutorial can be useful as it describes all the steps required to add new animation/pose to the game in one of the easiest ways currently possible. No any Papyrus coding skills are required here, but just simple copy&paste activities mostly. No more, no less.
Adding new animations through Fore's modified behavior files and Director's Tools esm as a base does have some benefits:
- animators can spend far more time on creating animations than "wasting" it to mess with the Papyrus code, and as a "bonus" their animations receive access to some native functions of Director's Tools mod - chains/queues of anim events, memorization, and synchronization.
- players, photographers of virtual worlds, and machinima directors on the other hand, receive a "common animations/poses platform" - no matter how many animation mods based on this solution they have installed, all is always accessible in game from one and exactly the same menu.
SOME IMPORTANT INFO:
Bear in mind that technique described in this tutorial isn't the most ideal. Behavior files are prone to change because of Bethesda updates, and while many such mods may be created which could use Director's Tools as a base, they won't have access to all its features when loaded together. Of course each of them will have its place in main menu of DT and the basic functionality that allows to trigger animations will be there, but which of these mods will find its way to Custom Animations menu its decided by mods load order. And only that place allows to add new animations to queues, memorize and synchronize them.
Well, sill it's better than nothing... but definitely not an obstacle for an avid machinima director or any of skyrim's paparazzi ;]

