No, it is not possible to put Actionscript 2.0 code in an Actionscript 3.0 code file. The Actionscript virtual machine that runs Actionscript 3.0 code is completely different from the Actionscript 1.0 and 2.0 virtual machine. The only way to include Actionscript 2.0 code in an Actionscript 3.0 project would be to have the Actionscript 3.0 Flash file load an external Actionscript 2.0 Flash file.

Adobe Flash CS4 does support Actionscript 1.0. The Actionscript 2.0 virtual machine fully supports Actionscript 1.0 code. Simply choose the Actionscript 2.0 file format, and code any Actionscript 1.0 code you wish.

Adobe Flash and Adobe Flex both come with Actionscript compilers built in. There are also some stand-alone Actionscript compilers. MTASC is a command-line compiler that can compile Actionscript 2.0 class files. SWFTOOLS also has Actionscript compilers similar to MTASC for Actionscript 2.0 and Actionscript 3.0. There are also some third-party Flash development software programs that support Actionscript compiling.

ActionScript 3.0 is the latest version of ActionScript, which is an object-oriented programming language and, therefore, cannot be purchased anywhere. One can find reference material on ActionScript 3.0 at the official Adobe website or one can find out more about ActionScript in general at Wikipedia.

You have to know actionscript. Go to Newgrounds.com for some actionscript tutorials.