Okay, here's a modified version of your .fla. I like the simplicity of your fla.
You also might want to consider responding to direct keystrokes, so the user doesn't have to hit the 'guess' button.
I've simplified your code somewhat, and eliminated the sub-routine that returns the array of correct letter positions - it was making things overly complicated.
Also implemented your game reset, and game win detection.
I attached your text fields to your movieclip 'word' (the same one that the dashes are attached to). This way, it's easier to reset the game by deleting the 'word' movieclip (which deletes everything attached to it). By doing so, I had to change the letter coordinates so that they are relative to the position of word.