[Flash] Exporting Movies to GIF!

Seemingly simple... but not quite.

I'm trying to make Christmas Avatars, and have got the avatar on layer1 and the falling snow on layer 2. Both have transparent backgrounds

I'd like to preserve the transparency when exporting the movie to GIF format, instead, I get the background of the working area.

How do I preserve this transparency?

I am attaching the FLA file here so you can take a look at it. If you export this current one as a GIF, you'll get a black background...