Hello there,
I just want to ask you if there is some simple tool or program which can convert nif files to obj format - so they can be opened in blender (or other 3d editor)

I've found some nif scripts addon to blender but only to version 2.49
If you know about some other ways how to convert those files please let me know

- I want to import some of my own 3d objects /mostly armor/ into morrowind

The only way I know of is to install Blender 2.49 and use it for converting from nif to other formats and vice versa and some other tool of your choice for actual modelling.