Microsoft Knowledge Base Article 323166 contains the following summary:

Learn how to download updates, enhancements, and Windows Hardware Quality Lab (WHQL) logo device drivers from the Windows Update Catalog. You can search the Windows Update Catalog to find updates (such as updated system files, service packs, new Windows features, and device drivers) to download and to install across your home or corporate network on Microsoft Windows-based computers that are running Microsoft Windows 98, Windows Millennium Edition, Windows 2000, Windows XP, or Windows Server 2003.

Specifically, you can learn how to do the following tasks:

Access the Windows Update Catalog by one of two methods.
Download updates from the Windows Update Catalog.
Download WHQL logo device drivers from the Windows Update Catalog.
Locate your downloads in your download history.
Use Windows Update and the Automatic Updates service to configure a server on a corporate network to provide updates to corporate servers and clients.
Use the Automatic Updates and the Critical Update Notification service to keep computers up-to-date.
Troubleshoot any problems that may occur when you use the Windows Update Catalog.