When using the Upgrade CD-ROM, setup prompts you for the CD-ROM of the previous version of Windows NT. The compliance checker on the Upgrade CD-ROM does not recognize Backoffice 4.5 as a valid media.

You will have to wait till Windows 2000 Service Pack 1 is released.

To perform the upgrade, you must copy Setupdd.sys, from SP1, to the second setup boot disk, or to the distribution share point.