Fglrx is not fixed for ubuntu 12.10. It should breaks your graphics(only for 12.10). It's better to wait for fix.
Now to use open-source driver properly, follow the steps1. Remove your existing fglrx driver
sudo apt-get purge fglrx*Open /etc/default/grub
sudo gedit /etc/default/grub
Replace the line GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" with
GRUB_CMDLINE_LINUX_DEFAULT="radeon.modeset=1"
Save and close the file and update your grub
sudo update-grub
Reboot. To check driver is working or not install mesa-utils
sudo apt-get install mesa-utils
Now go to system setting>Details or system info. Check on Graphics section. It should be Gallium