I have a proprietary device connected via An arduino microprocessor to USB, which I want to use as a Mouse emulator. At present I use a processing program to generate x,y data based on the arduino output

I'm looking for a way to emulate the mouse, so that a flash application such as a game which uses the mouse pointer can be used with my system, without altering the application. Assume that the applications are already developed, and cannot be edited. 

Can someone suggest what i need to interface with my processing application ?