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Yeah, but you have to customize the header.php file to get it to work. Basically you need to make a db call that will fetch the users avatar, then write it to a smarty variable which can be used in your theme. Ive done it with excellent luck. If you would like, I could look into modifying the header for you so that you could do it.
The site that I've done is on is my bf2online site. It does what you are asking in another way. It takes the users rank and applies it in a way that will display the users rank in a string of text next to the username along with a country of origin flag. It also changes the header image based on rank. Essentially, its the same principal.
Just let me know.