go to your profile in the link to off site avatar type the url of the picture you wish to use. The picture has to be loaded onto the internet for it to work I use www.imageshack.us free and you dont need to sign up. upload the image from that link right click the picture go to properties and copy the url. one you have done that add the url you have copied into the profile where it asks you for the link.
this is the same with the signature banners but you add the code into the signature box like so
[**img]http://www.linkofyourimg.jpg[/img]
take the stars out they r there to show you the code