Trouble wrapping mind around AS3 and Arduino comunication

Hello! I hope someone with good hart and patience will read this. I have been trying to get into Arduino world for some time and have gained some progress with it. I'm also quite experienced with Flash AS2/AS3 and I did get most of AS3 to Arduino examples working. The problem I'm having is to understand basic programming to send data between Arduino and AS3. What I would like to do is to have two separate programmes running on Flash and Arduino that could exchange data (longer than 1 - 127) both ways. I did Glue/Firmata, but it sends commands straight to pins. I did try messenger but just couldn't get my head around samples to get it working properly. I have Mega.

I would be extremely grateful if someone could point me to or give the most basic code, tutorial or forum topic that would teach me how do something like this: 1 Arduino receives 2 numbers from Flash; 2 adds them together; 3 sends result back to Flash.

Thank You! Janis