Ive been using Actionscript 3.0 Game Programming University (which i actually got because of a post on this forum, in the coding section i think). Its not meant for beginners, but provided you have some idea behind the theory of programming (arrays, variables, etc), you should be able to get the jist of what everything does. That is, if you are intending to use it for games. There are plenty of books about actionscripting. A quick look at amazon will help.
Link to the Game programming book (from the other post):
http://www.amazon.com/ActionScript-3-0-Game-Programming-University/dp/0789737027/ref=sr_1_1?ie=UTF8&s=books&qid=1234397169&sr=1-1Link to coding forum:
http://www.biteycastle.com/smf/index.php/board,20.0.html