I developed a Single player game in Flash (Tic Tac Toe) and in the Multiplayer mode i will be able to do both player playing on the same system with out network.

I would like to extend it and make it enable to play the Multiplayer game for two player playing it online.

How i can be made give me some ideas , How test the Multiplayer game playing along with different computers(I do not have internet connection in home).

How I able to change the single player game into Multiplayer game , any minor changes required or I have to change the code base completely.

In which way i can make it possible.