In KB article Q154538 Microsoft asserts that a "WinNT 4.0 Upgrade CD Will Not Upgrade WinNT 4.0". I have had some success by first editing:
HKey_local_Machine/Software/Microsoft/Windows NT/CurrentVersion
and changing CurrentVersion to 3.5.
Also edit:
Hkey_Local_Machine\System\Setup\SystemSetupInProgress
Double Click SystemSetupInProgress and set it to 0. Do the same for:
Hkey_Local_Machine\System\Setup\UpgradeInProgress
NOTE:It is best to uninstall SP2 or SP3 prior to an update
install. If you have RAS installed you must uninstall the SP. If
you can not uninstall, then:
expand <cd-rom>:\i386\tcpip.sy_
%systemroot%\system32\drivers\tcpip.sys prior to doing the
update install. The note is also applicable to installing RAS
after SP2/SP3.
