You need to have your original disks for this to work. Install ac2 in a folder of your choice. Go to the ac2config.exe and copy it. Next paste it in your downloaded ac2 install folder. Then go into preferences.ini. Scroll all the way to the bottom and look for RunConfigTool=0. Change this to
RunConfigTool=1 and run ac2. Now when you log in the config program will pop up and you can enable pixel shaders.