How to use the Windows 98 upgrade for a full version
You can use your Windows 98 upgrade CD provided you have your Windows 95 CD, diskettes, or the complete set of Windows 3.x diskettes. Start the installation of Windows 98. During the installation, you will receive an error message indicating that the setup process was unable to locate the previous operating system. Place either the Windows 95 CD or diskettes or the Windows 3.x diskettes into the computer and point the setup program to the appropriate location.