Sorry for the belated notice, this was turned loose on 6/3/08. Great news!!!!
Windows Installer 4.5 is now available!!!!!!
New and improved features in Windows Installer 4.5:
The following new and improved features have been implemented in Windows Installer 4.5.
Multiple package transaction
In a multiple package transaction, you can create a single transaction from multiple packages. In a multiple package transaction, a chainer is used to dynamically include packages in the transaction. If one or more of the packages do not install as expected, you can roll back the installation.
Embedded UI handler
You can embed a custom user interface (UI) handler in the Windows Installer package. This makes a custom UI easier to integrate. You can also invoke an embedded UI handler from the Add or Remove Programs item in Control Panel. Or, you can invoke an embedded UI handler during a Windows Installer repair process.
Embedded chainer
You can use the embedded chainer to add packages to a multiple package transaction. You can use an embedded chainer to enable installation events across multiple packages. For example, you can enable install-on-demand events, repair events, and uninstall events across multiple packages.
Update supersedence resiliency
This feature lets you correct for changes in the FeatureComponent table during supersedence.
Shared component patching resiliency during uninstall
This feature makes sure that the most recent version of a component is available to all products.
Custom action execution on update uninstall
This feature lets an update add or change a custom action so that the custom action is called when an update is uninstalled.
For more information you can check the MSDN Documentation or the Windows 4.5 Installer Team Blog.
John Howell 