The Visual Studio Tools for Office build environment in Visual Studio 2008 relies on a number of MSBuild tasks used together with the Microsoft.VisualStudio.Tools.Office.Office2003.targets and Microsoft.VisualStudio.Tools.Office.Office2007.targets files. These tasks register add-ins, generate the application and deployment manifests, copy customized documents to the build output folder, and update security on development systems.  Be sure to create a backup copy of these .targets files before modifying them.

The build tasks are documented in Microsoft.VisualStudio.Tools.Office.BuildTasks Namespace (2007 System). However, the (2007 System) name appended to the build task name is not always correct. For several reasons, the build tasks for Microsoft Office 2003 and the 2007 Microsoft Office system were merged into a single namespace. The following tables show the correlation between the specific build task and the Microsoft Office version.

The following table shows which build tasks apply to the 2007 Microsoft Office system.

The following table shows which build tasks apply to Microsoft Office 2003.

[Updated 25 Aug 2008] Unlike what the following comments say, you can build VSTO solutions without having Visual Studio installed.  Kent Boogaart has documented the assemblies that you need to copy at http://kentb.blogspot.com/2008/08/building-vsto-projects-without-visual.html 

Mary Lee, Programming Writer