Hy,
The getAvatarMovieClip function return a MovieClip.
As far as I'm checking know the os performance with Flex builder 3,
I was wondering- do you know how (using AS3) can I format or cast it
to UIMovieClip
If your avatar class extends UIMovieClip (which in turn extends MovieClip), then yes, you can cast the object returned by the getAvatarMovieClip method to UIMovieClip.