About the program probably the best is Adobe CS5(If you want to continue earning money and making games in flash since it's 700$ or something like that) - But still if ur not sure, I mean there can be some problems after you buy the product and then you can't learn Actionscript 3.0, that would be a huge waist of money.
Flash Develop is free and probably best free software out there, not beginner friendly tho.
- Only language for making flash games is ActionScript.
- Hope I helped, Cheers, Reamon.