As a general rule, users should change their passwords at regular intervals for security purposes. While encouraging users to change their passwords regularly is a good idea, this often leads to issues with users forgetting their passwords. Since resetting passwords for other users can quickly become a pain if you constantly find yourself doing it, XP includes the ability to disable the Change Password button found on the Windows Security dialog box.
To disable this button, open Regedit and browse to the HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System and HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Policies\
System keys and create new REG_DWORD values named DisableChangePassword in each. Configuring a value of 0 will allow the user to change their password, while a value of 1 will disable the Change Password button, forcing them to use their current password. In most cases, good security practices would dictate that you grant a user the ability the change their password. However, in the case where a user insists on using a poor password, this allows you to control the password that they much use (hopefully a strong password), without the fear of the user changing it.