Changing User Passwords with Outlook 2003/2007
Generally speaking, Outlook 2003 and Outlook 2007 have a built-in mechanism that allows a user to change their password.
In Outlook 2007, you find this (almost) hidden capability at Tools -> Options -> Other -> Advanced Options -> Custom Forms -> Password. In Outlook 2003, it is in about the same place. However, this is buried and almost impossible to find. If you want to change the user's password, and you are directly connected to the Exchange server (and in that same domain), then using Start -> Windows Security -> Change Password is much easier.
However - that capability does not work if you are using Outlook with RPC/HTTPs. The capability discussed above uses the Win32 API to effect a password change, and that does not work when you are using RPC/HTTPs.
Therefore, if you want to change your password when using RPC/HTTPs you really have three choices.
1) Call the helpdesk - the most likely scenario if you are not in a hosted environment
2) Use the control panel - most Hosted Exchange providers provide a function on a user's control panel enabling the user to change their password, using the functionality in item (3). Most large companies will implement a similar capability for their users. Small companies will likely need to implement item (3) directly or their helpdesk will do it (as in item 1).
3) Enable IISADMPWD - use KB 555071 to enable the use of a web page to allow changing the password of an active directory user.
[The Windows 2000 version of the article is KB 269082. While a Windows 2008 version of the article can be presumed, it is not available as this article is being written.]