I received a bunch of mail over the weekend indicating that the SP5 release I mentioned earlier was in fact a release candidate, not the final release. That's not the information I have; in fact someone from Microsoft told me over the weekend that it was indeed the final build. And it appears that the release I mentioned earlier is indeed the final version. No matter: Microsoft is now offering the final release of SP5 for Windows NT 4.0 in both 40-bit and 128-bit versions from the Windows NT Web site.
According to Microsoft, Service Pack 5 (SP5) provides the latest updates to Microsoft Windows NT Workstation 4.0 and Windows NT Server 4.0 (including Enterprise Edition). SP5 contains known Year 2000 updates for Windows NT 4.0. These Year 2000 updates are also available as separate Web downloads that customers may apply to a Service Pack 4 system. Providing these options gives organizations the flexibility to choose which path is easier for them to address Year 2000 issues. SP5 is not a required upgrade for Year 2000; Microsoft recommends that each customer consult the SP5 documentation and then determine whether to deploy it.
And because the service packs are cumulative, you don't need to install a previous SP to upgrade to SP5: This release includes all of the fixes from previous SPs