1) Exit World of WarCraft completely.
2) Click
here to begin downloading Wintergrasp Map. Extract the zip file once the download is complete. (Right Click the Folder and select Extract)
3) Place the folder in your World Of Warcraft Addon directory. This is usually one of the following:
C:/Program Files/World Of Warcraft/Interface/Addons/
C:/Users/Public/Public Documents/Blizzard Entertainment/World Of Warcraft/Interface/Addons/
(For Windows users, go to Start and select Run. Copy one of the file paths above and select OK. This should bring up a window with several folders. Drag the Wintergrasp Map folder and place it in the window.)
4) Run World of WarCraft. If the above steps are performed correctly there will be an Addons button on the character select screen. Make sure the addon is enabled.