I've seen a few hundred posts asking how to make a game, and no responses showing how to do it for free, so I'll help out anyone who seriously wants to program a game in Actionscript, and not spend $699 on Flash CS3.
1) Download the Flex 3 SDK from Adobe's website. This includes the mxmlc.exe compiler to create SWF files. Cost: $0.00
2) Download the latest version of FlashDevelop. It'll really help with writing actionscript, organizing files, and using mxmlc.exe, the SWF compiler included in the Flex 3 SDK. Cost: $0.00
3) Read up on programming in Actionscript 3.0 (or 2.0 if you want). Senocular has a great intro to using mxmlc.exe and as3 here.
The downside? You have to import all your graphics, or draw things in code.
The truth is that Flash is too expensive if you are just going to be messing around and making small animations and games. I purchased CS3 when I started making games for money, but before that I did/could not pay for flash. I started when I was 13, and I could not afford it back then. And it would not have been worth the money for what I did. 60% of Adobe product users did not pay for what they use.
True, have a price tag like Flash's makes it very discouraging for first timers to get into Flash. None of us really know if we will get into flash enough to get sponsorships and I mean really, who has 900 bucks to spend at the age of 13ish I sure as heck didn't (and still don't )
What I did, and what I continue to recommend to begginers, is to start off by getting either a student version and/or older version of flash, at the time I started I went to ebay to look for a slightly older version of flash, and found Macromedia Flash MX 2004 (which was 1 version older than the lastest version at the time) -it was only like $150, I save up and bought it and it was totally worth it too. So yea, don't get discouraged guys, just try to find those workarounds so that you may to enjoy the wonderful world of Flash
If you want to make free stuff use game maker. But wasting your time on a free adobe like product is no good. It's teaching people to be cheap and not do what they should be properly doing, it's dumb to advocate this.
I have CS3, and it is worth the money. The drawing tool is amazing! By the way, you can actually create a game entirely in code. You can make objects and lines using something called "API". Here is a game made entirely of code. If you want to create objects using code, here is a tool developed by the same user. It will actually show you the code necessary for creating the object you designed.