Windows Installer 4.5 for Vista SP2 & Windows Server 2008 SP2, 5.0 for Windows 7

Microsoft released Windows Installer 4.5 on the Microsoft Download Center for XP SP2+, Server 2003 SP1+, Vista, and Server 2008. Now, with the release of SP2 RC-Escrow build, it has been confirmed that the new version will also be bundled with the SP2 for Vista and Server 2008. Windows Installer 5.0 is right now only available in Windows 7 and Windows Server 2008 R2 (download link), which are both in beta.