Since the installer for LabVIEW is based on the Microsoft Windows Installer Service, sometimes the version of the service installed on the machine is older than the one required by the LabVIEW installer. In some cases, the Installer Service itself is not installed. This can be the case with Windows 95, 98, Me, NT, and 2000. Simply install the appropriate version, reboot your computer, and retry the LabVIEW installation. The installer is on the LabVIEW 6.1 CD and is named instmsi.exe.