[h-e-w] can't run 'ediff'

[Zahar Malinovsky]

i have emacs 21.2 on Win2003.
After "M-x ediff-files"
It says "Searching for program: can't find directory or file, ediff.
My PATH variable is set to d:\emacs-21.2\; d:\emacs-21.2\lisp; d:
\emacs-21.2\site-lisp

What is wrong that it won't run?