First of all forget about AS 2 - nobody is using this old fashioned language.
So starting with AS 3.0 you need Flex SDK if you want it open-source, so:
http://opensource.adobe.com/wiki/dis...xsdk/Downloads
Then you need to choose your IDE (flex is just an command line compiler + libs), two option are good your attention:
- FlashDevelop - it's a nice one but works on Windows only and you will need to configure it a bit
- Flash Builder (standard version) - based on eclipse (which you like), costs $249 (which you don't like) but there is no better solution for AS 3 development. Of course you can try to find some "patched" version for free

After all you need a book to start learning, so:
http://help.adobe.com/en_US/FlashPla...t/3/index.html - believe me it's the only reliable source of knowledge
My little advice before you start working with apps based on Flex components, etc... Try to build few pure AS 3 applications just to avoid frustration at the beginning
When you are ready with the IDE (and done at least "Hello world" app) feel free to ask me directly... I have few years experience dealing with complex flash based apps so I think i can help