Alright, after downloading, you'll need to decompress with the files with WinRar. Right click the file you downloaded, and select Extract Here. Two .hak files should show up, select them, right click, and select Copy.
Go to My Computer, then whatever hard drive you have your NWN folder in, open your NWN folder, go to the 'Hak' folder and open it, right click, and select Paste. You should have the two .hak files you downloaded in the folder. You're done from there.
