I have 1 1920x1080 display that I am using as a primary display, with a 1600x900 display off to my side. I have tried to set up the smaller display to be positioned to the right of the larger display, but I can't. The only option that works is to use it as a clone. When I connect the smaller monitor to another DVI port on my AMD Radeon HD 6950, it doesnt work at all.
I can provide more information if needed.