Microsoft Knowledge Base Article 317380 contains the following summary:
This article describes how to use upgrade packs to upgrade to Windows 2000. If you upgrade from either Microsoft Windows 95,
Microsoft Windows 98, or Microsoft Windows Millennium Edition (Me) to Windows 2000, you may have to use upgrade packs
(also known as migration dynamic-link libraries \[DLLs\]) because of registry and program differences that exist between
the operating systems.
You are prompted for additional upgrade packs that are not included on the Windows 2000 compact disc (CD) after you start the upgrade process. You may have to use additional upgrade packs for certain programs to run with Windows 2000. These programs either do not support Windows 2000 or they introduce problems to Windows 2000. Before you upgrade to Windows 2000, check with the software manufacturers for any upgrade packs that may be available. If an upgrade pack is not available for a program, you may have to remove the program before you upgrade to Windows 2000. Use the Add/Remove Programs tool in Control Panel to remove the program. After you upgrade to Windows 2000, either reinstall or upgrade the program.