I just discover at O’Reilly that the new book from Colin Moock is out in “Rough Cuts Version”.
It’s really time to learn AS3 and even more for people only used to develop using a non object oriented programming language.
The publication date for Essential ActionSript 3.0 is in June 2007, but with rough cuts you can already read some chapter.
If you are more in a hurry with AS3 you can also check the really good “ActionScript 3.0 Cookbook” (By Joey Lott, Darron Schall, Keith Peters ), this one is already out of stock at the time I write, but printed. Maybe your are lucky enough to find one in your library.