Instructions
Open Windows Explorer.
Navigate to the folder that contains the mod that you want to install.
Right-click on the mod folder and click "Copy."
Navigate to the "C:\Program Files (x86)\THQ\Stalker\gamedata" folder.
Right-click in an empty portion of the folder and then click "Paste."
Start the Stalker Shadow of Chernobyl game and click on the "Mods" button on the main menu, check the box next to the mod you installed and then click "OK" to activate it.