Ok, what you must understand is that ATT is another program, which comes with the drivers, packaged, kind of like CCC comes w/ the regular drivers. For instance, I set all my settings through ATT and don't go to display properties, advanced. (In fact you shouldn't do this if you have ATT, just do eveyrthing through att)
That said, it should have asked you at driver installation if you want to install "ATi Tray Tools" (ATT) and multires. I usually just install ATT. Did you do this?
If you did, it does not start up automatically at first. Go to start, programs, radeon omega drivers, and you will find ATT there. Start it. It will appear in the bottom right. Right click it, set the setting I told you. After that, right click it, go to hardware, overclocking.
MAKE SURE powerplay is not on when you overclock. You can tell when powerplay is on b/c the clocks will be at 99/120 instead of the default 297/229.50