Very nice prg to decompile and modify swf, it's part a freesource project:
http://www.softpedia.com/get/Programming/Other-Programming-Files/Yogda.shtml
latest version is 1.0.564
Give it a try is really a great prg.
I think is better than any other decompiler (broken image removed)
This is the home of developer http://www.yogurt.com.tr/