This is VERY hard. The Fritz level, i.e. Level 6 computer, has an ELO rating of 1200.
I'll admit first off, I'm not a chess expert, so I used a downloadable program online, named "KChess".
Using this program, after selecting the difficulty (Expert), I selected "Play as Black". The KChess program will now play as White. You copy his moves in Battle Vs. Chess, against the Battle Vs. Chess computer, and then you copy the Battle Vs. Chess computer's moves into KChess.
So, basically, KChess is going to beat Battle Vs. Chess's Level 6 AI computer for you.
I tried for a while to get this by myself, but I'm just not that good, so I did it the above way.
If you can get it legit, congrats. If not, use this solution :)