We really recommend using the Fallout Mod Manager to install Project Nevada!
It will automatically copy the right files and take care of any conflicts with already installed mods.
So before you can get started, you have to choose whether you want to do the FOMM installation (recommended) or a manual installation.

Remember: The Core module is required in any case! If you don't like a specific feature, you can disable it in-game.

> Automated Installation with FOMM

1. Start FOMM and click on Package Manager.

2. In the top-right button menu, click on Add FOMod and select the downloaded archive file.

3. Project Nevada will now appear in the list. Select it and click Activate.

4. In the installer window, select the modules you want, then click Install. If you are prompted to overwrite anything, click Yes to All.

5. Done!

OR

> Manual Installation

1. Locate the Data/ folder in your Fallout New Vegas installation directory. Typically it's found at Program Files/Steam/SteamApps/common/fallout new vegas/Data/.

2. Extract the contents of the downloaded archive file to your Data/ folder.

In case you are using any mod that modifies the interface:
3. Locate the Data/optional/ folder. In there, copy the contents of following directory your Data/ folder, depending on which interface mod you are using:

4. In the New Vegas Launcher, click on Data Files and select the plugins you want.

5. Done!