In Windows® platform, Microsoft is committed for providing Help and Support technology that will also continue investigating new solutions for software developers. For four Microsoft Help technologies, i.e. Windows Help, HTML Help 1.x, the Help and Support Center, and the Assistance Platform client, the following information clarifies the support in Windows Vista® and Windows Server® 2008.
Windows Help (WinHlp32.exe)
Microsoft Windows versions from Microsoft Windows 3.1 operating system includes Windows Help (WinHlp32.exe) help program. This Windows help program displays 32-bit help content files having the .hlp file extension. You should download and install WinHlp32.exe from the Microsoft Download Center to view 32-bit Help files with the .hlp file extension in Windows Vista. For Beta 2 or RC1, this download is not available. Microsoft recommends software developers to discontinue using Windows support in Vista. Software developers shipping programs relying on .hlp files are encouraged to transition their Help experience to an alternative Help file format, such as CHM, HTML, or XML. You should also change your calls from the WinHelp API to the new content source. For converting content from one format to the other several third-party tools are available assisting authors.
HTML Help 1.x (HH.exe)
Starting with Windows 98, a Help system named Microsoft HTML Help 1.x (HH.exe) is included in Windows releases. HTML Help is used to display compiled Help files with the .chm file extension. It is shipped with Windows Vista and Windows Server 2008. However, it will only make critical updates to the system. For Windows Vista and Windows Server 2008 or future Windows releases, new features or feature improvements will not be added to the HTML Help engine.
Help and Support Center (HelpCtr.exe)
For Windows XP® and Windows Server® 2003, a help application called, The Help and Support Center (HelpCtr.exe) was designed. Compiled Help files with the .chm file extension are displayed by The Help and Support Center.
Assistance Platform client (HelpPane.exe)
A new Help engine called Assistance Platform client (HelpPane.exe) is designed for Windows Vista and Windows Server 2008. However, it isn’t compatible with any previous versions of Windows. Help files with the .h1s file extension should be displayed by the Assistance Platform client. The Assistance Platform client can be customized by system builders, OEMs, and enterprise customers under license agreement for Windows Vista and Windows Server 2008. But it can’t be used by 3rd party programs.
That’s some information on Microsoft Help Engines, thank you!