If you are running Windows, you can use
<span class="podkreslenie">ARF2</span> to install a downloaded copy of CEP2.3 for you. When the dialog box comes up for updating, you just have to select "Use Local File" for the Community Expansion Pack rather than having it download again from the Vault.
ARF2 can be placed in a subfolder of your NWN folder (i.e. GOG.com\Neverwinter Nights Diamond Edition\ARF2). You can ignore all the stuff related to Higher Ground if you want.
Otherwise, as superfly said, the file extension of the files in the CEP package are named after the folders they should be placed in.