In 10.1.5, by typing "ps -axwwwww | grep ppp" in the Terminal, you can see the password of the dial-up account (if you're already connected). I know of no method of hiding this in 10.1.5 ... but in 10.2 (Jaguar), the passwords are now hidden.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20020923045810804