Look at this Tut video -> http://www.youtube.com/watch?v=aXtjyp1eRo0&fmt=22
Its about custom vault door's but it deals with DDS files etc because it deals with editing. If that's not what your looking for, clarify a bit and I'll try to refine it.
If you need to open the .bsa files to get to the files you may need, try this -> http://www.fallout3nexus.com/downloads/file.php?id=34
Edit: Here is a Nif viewer and editor -> http://sourceforge.net/projects/niftools/files/nifskope/
As for DDS:
Nvidia DDS / Normal Map Plugin:
Allows you to use Adobe Photoshop to open and edit DDS files.
The plugin will also create Normal Maps -> http://developer.nvidia.com/object/photoshop_dds_plugins.html
I just clarified on my own, the first vid might still be useful.