I'd do a thorough uninstall, using Driver Sweeper in Safe Mode. It's pretty simple. Just run the uninstallers for anything ATI, and then boot into safe mode, run Driver Sweeper and clean out the remaining files that are related to ATI. Then boot normally, and run the ATI setup for 10.8.
Directions are here:
Driver Sweeper @ Guru3D
There is one piece of ATI software called 'Catalyst Install Manager' which doesn't have an immediate uninstall link that appears in Add/Remove. You have to click 'Change' and go through a couple menu screens to find the 'Remove' option. Just a heads up, as I had trouble with removing that file a couple days ago.