In order to use the Gallery, go to the User Control Panel...
Select the Profile tab, then "Edit avatar"
There is now a button that says "Display Gallery". This will bring up the preloaded avatars.
Once there are more, you can then choose between categories. Currently, the only category is Holiday, as that was my test category. We will be adding to the Avatars like we do the Smilies, and will be announcing when we add more.
If you have any questions, please let us know.