If you try to change the password for a Keychain using the Keychain Access app, you'll notice on the resulting dialog box a circular button with an 'i' in it, as seen in the inset in the screenshot. If you click on it, Panther will display the Password Assistant panel (the remainder of the screenshot), which will advise you on the content of your password.
[robg adds: The advisor is pretty intelligent. If you use your name, it tells you. It checks words in the dictionary. It checks variations on words. If more people used tools like this, we've have less hacking ... he writes as he goes to work on his personal 13.1 password security score!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031026012223557