Patch management for the legacy operating systems (not supporting Windows Update functionality) are available through the Microsoft Download Center at the following locations:
for Windows 95, visit http://www.microsoft.com/windows95/downloads and for Windows NT 4.0, visit http://www.microsoft.com/windowsnt/downloads for Windows NT 4.0
Windows patch management can be conducted manually in Windows ME, 2000, XP, and 2003 by using Windows Update.
It works by having your computer connect to Windows Update servers automatically and receive a list of missing patches, based on a comparison of the client configuration data (such as operating system and Internet Explorer versions, hardware plug-and-play information, regional and language settings, and patch-level status) against Windows Update Catalog (located at http://windowsupdate.microsoft.com).