I found a simple way to code in AS2 for a multiplayer game, using the API even, which is in AS3.

This is an ActionScript "bridge" component, which allows direct imports of as2 based SWF files into your as3 file.

Some additional coding is necessary for communication between the two, but not too much and it is documented well enough. What this component does is amazing! Drag and drop the "container" into your AS3 .fla and the "terminal" into your AS2 .fla. If you place them both at (0,0), it will import the as2 swf file directly into the as3 swf at the exact location.

As an example, you can place a "window" component in the as2 file and make it work properly inside the as3 one, where the window component doesnt even exist!

Just thought I would share, since this is completely amazing!