Hi Mark,
I'm shooting with a Canon, but I am assuming that your NEF files are the RAW files in for Nikon? When you say conversion, do you mean getting them into a jpeg or photoshop format of some sort?
If your raw files are in 16bit, you will need to convert them to 8 bit to save them as Jpegs.
Also to clarify, RAW files are uncompressed, 'raw data' if you will, whereas jpeg files are still images that have been compressed to the standards of the Joint Photographic Expert Group (JPEG).
Hope this helps.