ZRF file is based largely on Chess.zrf, found in Zillions distribution.
Actually it is a standard chess, but black pieces are made invisible.
I have only Zillions version 2.0, but I think it should be easy to make it
work for older versions of Zillions.
First thing to try is to replace (version '2.0') in ZRF to something like
(version '1.0') or whatever you find in Chess.zrf in your version. You can
get error messages about not found images. Get them from demo versions of
Zillions 2.0 and copy them either to installation directory of Zillions or
to directory where you extracted Kriegspiel.zip file.