Saving file using ActionScript


I 've created a presentation in which the user can draw whatever he can. In that I 've a button named SAVE. On clicking that I want to save the image which is drawn by the user to his local hard disk. Can u guide me how can I give the actionscript for the button SAVE to save a particular file or whatever displayed, identifying the local c or d drive with a default saving dialogue box appearing to save that.