Microsoft’s new Vista operating system and Forefront security family don’t support legacy Microsoft apps. Microsoft hasn’t said which apps will not work with Vista or Forefront. Forefront may not run on Windows 95/98/ME or NT 3.5, 4.0, or 2000 with some Service Packs. Organizations running these older apps will have to use security tools from third-party vendors instead. Security experts question whether Forefront will use common dynamic link libraries (DLLs) DLLs are essentially files of system controls and drivers.”]
Source: https://www.darkreading.com/analytics/the-vista-forefront-security-two-step