Tried to run the first Witcher (EE, via Steam) using sweetfx and the "configurator", but I'm seeing no difference. I have successfully used it previously with Assassin's Creed 3.
I installed it on the game root folder and also tried to install it on the Wictcher\system folder, but neither works.
For reference, I used the most recent version of SweetFx with the configurator bundle from:
I was unable to find any game-specific instructions for The Witcher.