DDS
From NWN1 Custom Content Guide
Overview
This is the DirectDraw Surface (.dds) file format. It is used in NWN to provide high-resolution textures, utilising the compression and mipmap features of the format.
Though I cannot confirm this, some people have stated that care should be taken in choosing tools to work with DDS files, as many produce DDS's specific to other games and won't work in NWN.
