[h-e-w] pb with the use of Merge

[LaurentHelpEmacsWind]

Dear Emacs for windows list,

   I use GNU Emacs 21.3 and I have a problem when I try to merge two files with the Merge 
menu. When I type "n" in the control panel to find the first difference I have 
the following message :

            /cygdrive/d/cygwin/bin/diff3: subsidiary program 
`/usr/bin/diff' not found

        Since I can't install any software on my C: disk I installed 
emacs in D:\emacs directory and the cygwin programs in d:\cygwin and I 
added "d:\cygwin\bin"  in my PATH.

 May somebody help me to make Merge work.

On the other hand, I would like to add that the Compare (Ediff) menu 
works fine.

Best regards