Don't use ATI.
But if you do:
- sudo aticonfig --initial --dtop=horizontal - Make it use fglrx driver
- sudo invoke-rc.d gdm restart
amdcccle is a useful control program but wasn't necessary with the steps above
Here is a set of steps that worked for me the second time I had to go through this:
Make any working configuration with the "fglrx" driver (just enough to run amdcccle). The aticonfig program worked for this.
Run amdcccle as root. Go to the monitor configuration, multi-monitor area, and select "Single display with monitor N".
- Restart X.