Someone just sent me an email saying they couldn't get my method to work. I've used it on like 4 different versions with no problems. They stated they are trying to use it as:
/z-wD:\software\applications\wpi\ati\decoder
I haven't had much luck with long paths in the command. You must remember this install is thinking it is pulling from a CD. I usually copy it to a folder right off the root of C: like C:\Decoder or something and it works fine. Also remember this doesn't work on the package you download...they put checks in there that this doesn't fool. You have to first have a valid CD and run the downloaded package to get the EXE file that installs it. This app also checks for a valid CD and can be fooled with my approach. Thus, I also cover my butt with ATI in that you need a valid CD to do it in the first place, then those of us with legit copies can run it in silent, etc after it is extracted/downloaded with the package.