[AS3]Centering external sprite

I have a button.
It is 64x64
I also have sprites to load into those buttons
These sprites are inconsistent in dimensions
I load those buttons in.
I scale them down to fit in the 64x64 buttons.

Now the question is , how do i centre those sprites? I want them right smack in the middle of the button.

It is also important to note that these sprites are in the form of swfs. And also, the sprite itself can be anywhere in the swf, are of any size, and also extend into negative coodinate spaces.
Please help thanks.

edit:never mind… i think i got it…getBounds / getRect should do the trick…