I'm having trouble with a dual display on 11.10 also. I have an ATI
display card with a digital and a vga port. I was able to get it
working by not activating the propitiatory display driver. The dual
display is working great but I can't configure the special effects in
Compiz but I'm willing to go with the plain set up as long as the dual
display system works. I can't live without it.