If you set a master password on OSX 10.3.x, it will allow you to reset any users password without booting from the Install Disk -- this is particularly useful in a lab environment, or with users that are likely to forget their password on a regular basis.
You don't have to have FileVault turned on to enable a master password; just go into System Preferences -> Security and set the master password there. To reset a password without booting from the Install Disk, simply incorrectly enter the users' password three times at the login screen. You will be asked if you want to reset the password for this user. Enter the master password when prompted, and proceed to reset the user's password.
Saves a good 10 minutes over booting from the Install Disk!
[robg adds: Obviiously, as an admin, you can simply change users' passwords from the Accounts panel. However, I think most labs will not leave their admin accounts logged in, so you'd have to first login, then open System Prefs, etc. The method described above will definitely be easier if you've got a non-logged-in machine and a user saying "I forgot my password." Repeat that 50 times a day, and I can see how this could be a huge timesaver!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040901071448813