Wendersnaven.com (a resource for nwn2 builders)

The number of file formats, and where those files go, can be a bit confusing. Here is some basic information.

Files

A great place to start on what each type of file format is for is the File Formats page at nwn2wiki.

Some additional information about a few types can be found under this page.

Folders: The Basics

My Documents

All user data is meant to go in your My Documents folder. The default place for this is "C:\Documents and Settings\Sean\My Documents\Neverwinter Nights 2". This is where you put all files for modules and custom content that you download from the Vault. This is a big change from NWN1 and it has confused some people. Generally all this content come with instructions for how to install, but here is some additional information:

• ambient - Custom ambient .wav files.
• ambient_X1 - Custom ambient .wav files for the first Expansion (Mask of the Betrayer). I have no idea why this folder exists.
• Campaigns - This folder contains a folder for each custom campaign that you are creating or have downloaded to play. This folder contains content that the modules of that campaign will use throughout the game, most notably world maps, NPCs and items.
• Data - unkown
• database - In NWN1 they introduced what is known as a "Campaign Database." These are three files (.cdx, .dbf and .fpt) that allow you to store data between modules or outside of the context of a saved game. This was mostly used for Persistent Worlds. This has nothing to do the Campaign folders that were introduced in NWN2. Examples: The FRW Persistent Companion System uses these so you can save your companion information from one module to another.
• dmvault - I think these where DM characters are saved.
• erf - Erf files can be placed here. Erf files are used to export things (areas, characters, conversations) from one modlue and import them into another.
• hak - There is where hak files should be located for modules that use them to be able to find them. Hak Files are libraries of content used to override or extent the game and include custom content. Examples are the BCKII construction kit and the DMFI tools.
• localvault - Local characters are saved here. Character information is saved as a .bic file.
• modules - This folder holds .mod files, which are the actual modules.
• movies - A folder to place custom movies.
• music - A folder to place custom music, usually .bmu files. 
• music_X1 - Like the ambient music folder, I don't know why there is a custom folder marked for the first expansion.
• nwm - unknown
• Override - The override directory can "override" content in a module. It's a powerful way to add custom content, but developers are generally encouraged to use .hak files and campaign folders instead as the Override directory will affect all modules. In the wrong hands, this can have unforseen results. On the plus side, however, you don't need to compile the module to use the contents of the override directory.
• patch - I believe this folder is used when patching the game.
• portraits - Custom portraits can be placed here.
• prefabs - Prefabs are a collection of placeables and effects that have been packaged together, usually to make placing them easier. Lit candles and Dining tables are good examples.
• pwc - PWC files contain a module's walkmesh and pathing information for players. When you choose the "Create PWC" option from the Files menu in the Toolset, these files will end up here. They allow you to distribute this information to the players without requiring them to download the whole module. This is especially important for Persistent Worlds and DM run modules where you don't want the players to be able to open the module in the Toolset and cheat.
• Saves - This folder contains save game information.
• servervault - Players that have created characters in multi-player games that you host will have their players created here. Note that this only happens if you have the "Allow localvault characters" turned off when you set up the game.
• texturepacks - unknown
• tlk - All tlk files go here. They control the strings used in a module and are often used to translate a module into multiple languages. As I understand it, a module can only use one master tlk file. Most modules use the default. Most custom tlk files are edits to the default. Example: All spell names and descriptions are pulled from the tlk file, so custom spell packs need to get in there to add and edit the descriptions and names.
• ui - A folder for custom user interface files.

Program Files

All game data is meant to go in your Program Files folder. The default place for this is "C:\Documents and Settings\Sean\My Documents\Neverwinter Nights 2." All the files for the Official Campaign (OC) are also in your Program Files folder. Generally, you don't have to get into this directory, but the BIG exception is the plugins folder in the NWN2Toolset folder.  Here's the rundown:

• The Ambient folder - This folder holds the wav files for background noises. These elements are available across all modules. Note that when trying to decide what background sounds you want, you can play these directly from your preferred multimedia device, although I cannot say if there are any permissions issues when doing so with the Toolset open.
• The Campaigns folder - The supporting campaign files (scripts, images, etc.) are in the campaigns folder. These are files that are available across all the modules in the OC. These resources are only available to the OC.
• The Data folder - This folder consists of .zip files that hold data that can be used by the OC, and any other module, including those created by you. The 2da files, voice over wave, and many other resources are held here. These elements are available across all modules.
• The dmvault folder - Unknown.
• The Documentation folder - You should read this.
• The Effects folder - Unknown, but at a guess these seem to be basic effects that the Toolset uses.
• The hak folder - This contains your hak files. At this time, I am unclear if hak files go here or in the My Documents area.
• The Localvault folder - This contains the basic characters that come with the game.
• The Miles folder - Unknown.
• The Miles folder - Unknown.
• The Modules folder - The actual modules for the OC are in the modules folder. They are numbered and also have a descriptive name. These resources are only available to the OC.
• The Movies folder - Contains the .bik files that use present the movies (The logos and the into, etc.)
• The Music folder - This hold the bmu files for background music and combat music. These elements are available across all modules.
• The NWN2Toolset folder - Contains the source for the Toolset. Note that this also contains the "Plugins" folder. This is where you put community created plugins so that they are available in the Toolset.
• The Override folder - Will allow you to override some files, most probably in the OC. At this time, I am unsure what resources can be overridden.
• The patch folder - I'm assuming this is used during the patching process.
• The Servervault folder - Unknown.
• The temp folder - Definitely used during the patching process. Unknown if it is also used during gameplay.
• The UI folder - I think this is where you place your custom UI files, but I am not sure, as there is also one in the My Documents folder.
• The Utils folder - Unknown what these are for.

Discussion

There is currently a thread going on over at the Citadel about custom content and files.