This was only game I needed for 'Original Gamer' so I was getting frustrated.
This seems to work most of the time, I've played the computer five times and won all five times.
1) Go to: http://merrelles.com/English.html
or Google 'Nine Mens morris web game.' (1st Link)
2) Start Nine Men's Morris in AC3. Choose to go second.
3) On the flash game, choose the 'VII' difficulty, which should be smarter than the AI in AC3.
4) The moves that the AI makes on AC3 board will be the moves YOU play on the web game's board. So when the AI on the web game board moves, YOU will move your pieces on the AC3 board the exact way the AI on the web game board did, giving you the advantage.
In even simpler terms: Every move AC3 AI makes, (WHITE always moves first) YOU MOVE on the web game board using BLUE. Then whatever move the web game's AI makes on the web game board using RED, YOU move on the AC3 board using BLACK. Giving you the perfect counter.
If you have any questions please ask them, for I suck at explaining things like this.
Hope this helps. If you guys have any ideas on how the explanation could be clearer, let me know.