I have Emacs version 23 on Windows and it seem the ediff executable is missing?
From where can I download ediff for Emacs on Windows?
You can download diffUtils, extract it, add the path to %PATH% and emacs exec-path in your Emacs init file like that.
(when (string-equal system-type "windows-nt")
(progn
(setq diff-path "your-diff-path")
(setenv "PATH"
(concat diff-path ";"))
(setq exec-path
'(diff-path))))
finally, using M-x diff to compare what you want.