How to get Microsoft HTML Help 2 Compiler?

Where can I download the Microsoft HTML Help 2 compiler (or bounding SDK)? I want to generate HTML 2 documentation from my programming projects using Sandcastle Help File Builder and the Sandcastle Guided Installation wizard is instructing me to download that component.

Excerpt about HTML 2 taken from Sandcastle main page:

The HTML Help 2.x output includes a valid set of collection files and an H2Reg.exe configuration file to simplify deployment and integration of the help file into existing collections such as those used by Visual Studio.