WinHlp32.exe is required to display 32-bit Help files that have the ".hlp" file name extension. To view .hlp files on Windows Vista, you need to install this application.

Windows Help (WinHlp32.exe) is a Help program that has been included with Microsoft Windows versions starting with the Microsoft Windows 3.1 operating system. However, the Windows Help program has not had a major update for many releases and no longer meets Microsoft's standards. Therefore, starting with the release of Windows Vista, the Windows Help program will not ship as a feature of Windows. If you want to view 32-bit .hlp files, you must download and install the program (WinHlp32.exe) from the Microsoft Download Center.

Supported Operating Systems: Windows Vista; Windows Vista Business; Windows Vista Business 64-bit edition; Windows Vista Business N; Windows Vista Enterprise; Windows Vista Enterprise 64-bit edition; Windows Vista Home Basic; Windows Vista Home Basic 64-bit edition; Windows Vista Home Basic N; Windows Vista Home Premium; Windows Vista Home Premium 64-bit edition; Windows Vista Starter; Windows Vista Starter N; Windows Vista Ultimate; Windows Vista Ultimate 64-bit edition.

Source: Microsoft via Flexbeta