for the avatar, you just paste the address of the picture to the correct place in the profile page. (in the upper right corner is a button that gets you to your profile)
the easiest way to post an image is to copy and paste the address of the picture to your text, then "paint it black" with your mouse (I don't know the correct term), and click on the IMG button on top of the white box where you write your text in.
or you can just write it like this [img]address%20of%20the%20pic%20here[/img]
