Add or Remove Programs entry for Microsoft Document Explorer 2005.

From here:

"Document Explorer 2005 is a redistributable package that delivers the 8.0 version of dexplore.exe. This is the help viewer that is used by Visual Studio 2005, and by other products such as the Windows SDK. In previous versions of Visual Studio, dexplore.exe was installed as a part of the main Visual Studio MSI or as a part of the MSDN MSI, but in VS 2005, it was separated into its own standalone package, and it is installed as a prerequisite before the main Visual Studio MSI."