Was going to make a "How to Upload an Avatar for Dummies" thread, but then I accidentally closed the page, so I'm just going to go ahead and throw it all right here.
First,
save the image you want as your avatar. Next, go to
http://imgur.com/ . Then, at the top right, hit
Computer, and
select/open your image. Next, a big window will appear. At the bottom right of that window, you'll see a
check box where you can check off whether or not you want to
Edit your image after uploading it. You're going to want to
check off that box, then hit Upload. After your image is done uploading, you'll be given the chance to
edit/crop your image. Edit your image the way you want to, then at the top, hit
Save.
NOTE: Avatars cannot exceed 100x100. After you've saved the image, you'll see a bunch of junk to the right-hand side. You'll want to
copy the Direct Link (email & IM) link, then go to your
Forum Profile on the forums and
paste it into the box where you
Specify your own avatar by URL.
Save your profile by hitting Change Profile, and ta-da!