Ok, I suggest you start small then and forget about the Community Expansion Pack (also known as CEP) for now until you're comfortable with the rest.
I suggest you try installing this little community module,
The Sunken Shrine of Ahmenkatja by Jesse Sky, just as an example. It doesn't require the CEP or any hak files, you just have to manage downloading the archive file on the Vault page, opening it and extracting the .mod file within into you "MODULES" folder.
1. Click on the link given on the Vault page to download the .rar archive.
2. Assuming your computer uses Windows (XP, Vista or 7), press the Windows key on your keyboard (showing the Windows symbol on it) in combination with the letter "E". This shortcut will open the Windows Explorer. You should now see the directory structure of you harddrive in the left window.
3. Find your "DOWNLOAD" folder and click on it. In the "DOWNLOAD" folder, find the file you just downloaded, "The_Sunken_Shrine_of_Ahmenkatja.rar".
4. Double-click on this .rar file. Chances are you already have a program installed than can open archived files with that extension.
5. If Windows gives you an error message or asks you what program you wish to open this unknown file type with, go to step 6. If it automatically opens the .rar. file for you instead, skip step 6 and continue with step 7.
6. If step 4 didn't work, you need to download and install a free file archiver, e.g.
7-Zip first. Clicking on this link will dowload the 7-Zip installation .exe unto your harddrive. Find this file called "7z920.exe" in your "DOWNLOAD" folder, double-click on it and follow the instructions to install. After that, repeat step 4. In theory, it should work now.
7. Your file archive should now show you the content of the .rar file in a new window: In this case it should only be one file, named "The Sunken Shrine of Ahmenkatja.mod".
8. Click on the window of the Windows Explorer again, find out where your NWN folder is on your harrdrive (e.g. Program Files/NWN), click on it to open it, then open the MODULES folder contained in it.
9. Now switch back to the file archiver window by clicking on it, then move the mouse cursor over "The Sunken Shrine of Ahmenkatja.mod", press the left mouse button and keep it pressed while you move the mouse back to the "MODULES" folder in the Windows Explorer window. Once you let go of the left mouse key, the ,mod file you selected should automatically be extracted to your NWN "MODULES" folder.
10. Now start NWN, in the menu choose "New", then "Other Modules" and see if the window that opens contains a module called "The Sunken Shrine of Ahmenkatja". If so, congratulations, you've just installed your first community module. If you like, you can try to play it now, it's a short story and shouldn't take more than an hour to complete.
This all sounds rather complicated and inconvenient if one takes the time to write it down step by step (or maybe I'm just not good at it, heh) but in any case, it should come quite natural to you once you've done it a few times.