Click on "Profiles" on the main navigation bar. On your profile page click on "Change Options". On the options page click on the "Change Avatar" button on the bottom right of the page. At the bottom of the avatars page are boxes where you can attach or upload your custom avatar.
There is a strict limit on size, though. If the picture in your post is the one you want, you're going to have to shrink it way down to get it in there.
Gina L Wolfe
2.1.1 ball pythons (Hector, Kumasi, Angel, Cinque); 1.0 ringed python (Houdini, RIP Diamond); 0.1 jungle carpet python (Indira); 1.1 white lipped pythons (Raphael, Aaliyah); 2.0 Bearded Dragons (Buddha, Perdito)