I would help you, but you can't seem to decide if you're an Aussie or a Kiwi!!!!
I'm assuming a) you have the source code to the game, and b) you have the rights to the game.
If the game uses a game engine that's been ported to Android, this may be feasible.
If it's using it's own game engine that's been implemented with Microsoft technologies (like DirectX), then it will require a full port. How much needs to be re-written will depend on how well the game was originally structured.
If you're in the this second situation, I would say that the time and effort to learning Android game development and the time and effort to port the game would probably equal about the time it took to develop the original game.
Also if you're in the this second situation, now might be time to move to a cross-platform game engine. Then you can port your game to other platforms as well, including the iPhone.
Also don't forget to redesign your gameplay experience. No controller. No keyboard. Touch screen.