I have dual monitor too, use the nvidia system with a geforce 6600 GT (but it worked fine with my geforce 4200 2 week ago) ..
The problem is that CB is a bit instable when i go back to windows so I decided to use it in windowed mod and it work perfectly (ok I have a very good computer that help me playing in 1600*1200 while my desktop is in dual 1600 .. but it may work fine in lower resolution if you have less powerfull computer)