Take the folders: "materials", "models", "scripts", and "sounds" and put them into this folder: "C:\Program Files\Steam\SteamApps\Steam Id\Counter-Strike Source\cstrike". (You will be asked if you want to replace files. Click yes).
DONE if you wanted the black slide. For the silver slide, open the folder "Silver Slide" and put the folder "materials" into the same folder mentioned in step one. (You will be asked if you want to replace files. Click yes).