This tool is a set of tools for working with the Pre-requisite bootstrapper in Visual Studio that is used by Setup Projects and ClickOnce. There are projects to enable you to create your own "packages" to add additional pre-requisite installers to Visual Studio, and also to build a stand alone bootstrapper using MSBuild.

There has been two versions(one for VS2005 and one for VS2008) in the MSDN Code Gallery: http://code.msdn.microsoft.com/bmg

And there is a KB article talking about how to use add prerequisite feature of VS2005 version from codeproject: http://www.codeproject.com/KB/aspnet/Add_Custom_Prerequisite.aspx 

In my particular case: Windows Server 2008 and Windows SDK for Windows Server 2008 and .NET Framework 3.5. After compiling the BMG package, I just need to put the output folder in the directory: C:\Program Files\Microsoft SDKs\Windows\v6.0A\Bootstrapper\Packages, then my VS2008 can recognize the new prerequisite.

If you don't know much about VS Bootstrapper, you may want to read this for more insights:
Use the Visual Studio 2005 Bootstrapper to Kick-Start Your Installation
http://msdn.microsoft.com/en-us/magazine/cc.aspx