Hi, I currently am running Windows NT Workstation 4.0 Service Pack 6a on my HP Pavilion from 1999 that originally shipped with Windows 98 Second Edition. Everything seems to be working fine, however, the Rockwell Riptide PCI Sound and Modem Card doesn't work with Windows NT 4.0. It always complains about a memory error. The PC works fine with Windows 95 and other operating systems. It has a Intel Celeron CPU and a ASUS MEW-VM motherboard.