The Microsoft® Windows® Installer is an application installation and configuration service. Instmsi.exe is the redistributable package for installing or upgrading Windows Installer. Windows Installer 2.0 Redistributable for Windows NT 4.0 and 2000 supports Windows NT 4.0 with Service Pack 6 or later and Windows 2000. Windows XP contains Windows Installer 2.0 and therefore can't be installed or upgraded by this redistributable

Operating System - Windows NT 4.0 & 2000
InstMsi.exe - 1,822 Kb

Windows Installer 2.0 Redistributable for Windows 9X supports Windows 95, 98 and ME operating systems.

Operating System - Windows 95, 98 & Windows Me
instmsi.exe - 1,708 Kb