Command prompt is what used to be called a DOS box.
Click on your start button, go to programs, mouse over to
accessories and under that should be a DOS box icon
labeled Command Prompt. Click on it and a Dos box will
come up, probably defaulting to your root directory c:\.
Looking at your games directory in explorer should show you
the path you need. Just do a bunch of cd directory_name
commands until you get to your tools\unpacker\ directory.
You can then unpack individual files or groups of files (like
all the *.txt files) by following the instructions in the readme.

Best of luck.