Microsoft Knowledge Base Article 297121 contains the following summary:
This article discusses how to implement the Change Password feature in Microsoft Outlook Web Access (OWA) to allow OWA users to change their domain passwords. This article also describes some of the common troubleshooting scenarios where you might use this feature.
The Change Password feature is provided by Microsoft Internet Information Services (IIS). The Change Password feature is not specific to Microsoft Exchange Server. This feature in IIS is implemented through the IISADMPWD virtual directory. In Microsoft IIS 5.0 and in Microsoft IIS 6.0, you must manually create and configure this virtual directory. In Microsoft IIS 4.0, this virtual directory is created by default, but it must be manually configured.