About Windows Installer, the .NET Framework, and Visual Studio.
Windows Installer 4.5 is now available on the download center for a variety of platforms, including Windows XP SP2 and newer, Server 2003 SP1 and newer, and both Vista and Server 2008 RTM and newer.
The Windows Installer 4.5 SDK is also available as a separate download, and the documentation has been updated on MSDN as well. You might noticed that the SDK installation package has a familiar red motif.
If you participated in the betas, you might have noticed some changes to new features since Beta 1. The CustomAction table has a new column, ExtendedType - an I4 that currently supports msidbCustomActionTypePatchUninstall (0x0800). There's also been some bug fixes over past versions including 4.0 on Vista and Server 2008.
When it will be avaible on Windows Update?
There are no plans at this time to release Windows Installer 4.5 to distribution channels like Windows Update or Automatic Update. It is available from the Download Center and can (and will be for SQL Katmai) be chained as a pre-req for other products.