6.1 is supported by NI on 95,98,NT,ME,2000, and XP. 6.0 is supported on 95,98,NT,ME, and 2000. 5.0 is supported on 95,98, and NT. I don't think anything but LabVIEW 3.1.1 works on Windows 3.1 - 32 bit apps don't run on a 16 bit OS. Even though you probably won't get any official support for 5.0 on 2000, you might want to give it a try anyway.