After you've installed the modules, unzip the Authentication tool and run the offline_premium application. Depending on your version of Windows, you might get an "Are you sure?" message--select "Run".
Follow the prompts:
1- Pick the module you want to authenticate using the radial buttons
2- Go to your NWN folder (default C:/Neverwinter Nights/NWN/) and find nwncdkey.ini
3- Open nwncdkey.ini (if a pop-up asks what program to use, select Notepad)
4- Highlight the code found after Key1=
5- With the code highlighted, right-click & select "Copy"
6- Alt+Tab back to the Authentication tool
7- Click on the text bar at the bottom and press Ctrl+V to paste the CD key.
8- Click "Generate!"
9- Go to the folder where you un-zipped the program, and find the .dat file matching the module you just authenticated
10- Right-click the .dat file, select "Copy" from the drop-down menu
11- Open your NWN folder (same one where you found nsncdkey.ini) and open the "premium" folder
12- Right-click inside the premium folder and select "paste" from the drop-down menu
Repeat steps 2-12 for each of the modules you want authenticated. (Note, in Diamond Edition, some of the modules already have the correct .dat file, and you don't need to authenticate them.)
After you've authenticated everything, close (X) all of your folders and programs, then run the game and enjoy hours of new content play time.