Oh, that wont appear in your posts. Just in your profile, which if you look at your profile, it's in the corner.

No no, I don't want one of the usual avatars, I want the one I uploaded to appear.

As for why your avatar might not appear, make sure that you chose a base, and you hit that "save" button bellow the preview.

Why won't my avatar appear on my forum posts?! -_-;