Microsoft Windows Installer 3.1
is an installation service and application configuration for Windows 2000 and XP. It can manage applications with MSI extension. This means that they are packed with an executable file for the installation and the software's configuration. This version is for Windows 2000 and Windows XP to SP2.
For a more recent version, see you on Microsoft website: Microsoft - Windows InstallerWindowsInstaller-KB893803-v2-x86.exe is the installation pack for Windows Installer update.