Adobe Flash CS3 Professional is the new one I think.
To buy the actual program, (at least the newest one) I believe it's upwards of $400. Although, I think you can download like monthly trial periods which might spare you enough time to make a functional game. Assuming you knew how to make a game in the first place.
yeah. Cs5 is the lastest version, and you need to learn action scrpit. Which is hard. Its not something your going to get good at just spending 500 dolalrs on the program, then watching videos on youtube.
Its hard stuff. Not to scare you, but if you really want to get good, go find some classes at a local college or something.