The Zip file contains a folder called gamedata, unzip this folder into your Stalker CS root directory
If you have not used mods before, you will need to find your fsgame.ltx file in the "c:programfilesdeepsilverStalker Clearsky"The landscape has been redone to (hopefully) look more like an apocalyptic scene. This is only a beta so I have left out some of the less important things like new music in order to keep filesize down.