Microsoft isn't just getting ready to roll out Windows XP, it also has an update to Windows 2000 waiting in the wings.
Windows 2000 service pack 3 is showing up on Microsoft's anonymous FTP server as a collection of HotFixes. You can get an idea what fixes are in SP3 by cross-referencing the folder name on the FTP server with Microsoft's Knowledge Base articles, for instance, Q290321. Some of the newer folders are not publicly accessible, however, and the Q-numbers are not referenced in the Knowledge Base.
Although Microsoft hasn't given a release date for SP3, it looks like it will be sizeable update to Windows 2000. The SP3 folder has some 680 subfolders, many more than for previous service packs. The subfolders contain actual patches, in some cases over 25MB worth of files.
Many of the HotFixes are available from Windows Update, however, so customers who use that service frequently are looking at a much smaller update session.
The files in the folders with public access can be downloaded, but they are compressed archives with password protection. Passwords are obtainable through Microsoft Services, for a charge.