The Microsoft® Windows® Installer is an application installation and configuration service. WindowsInstaller-KB893803-v2-x86.exe is the redistributable package for installing or upgrading Windows Installer. 

Windows Installer 3.1 Redistributable supports Windows 2000 with Service Pack 3 or later, Windows XP, Windows XP Service Pack 1, Windows XP Service Pack 2 and Windows Server 2003. Windows Server 2003 Service Pack 1 contains Windows Installer 3.1 and therefore can't be installed or upgraded by this redistributable

Version: 3.1.4000.2435 
Knowledge Base (KB) Articles: KB893803  
Date Published: 9/2/2005 
Language: English