To get an avatar next to your name, you must go to [u] My Account[/u] in the menu bar on your left. In there you will see a section called [u] Change your Info[/u]. Halfway down the page you will see [u] Your Avatar[/u].
There are about thirty different ones in there for you to choose from.
If choosing one from there does not work immediately, you will then need to click on the word [u] Profile[/u] above (just beneath where it says, Forum, you are logged in as whoever.) In there you will see a similar form to the previous one. You will then need to select your avatar in there too (it must be the same one).
I'm not sure if you need to activate both forms at first, but I'm pretty sure both need to be filled in should you ever need to change your information/avatar etc.
Custom avatars are only available to members of Friend rank or higher.