http://support.microsoft.com/kb/917607/en-us
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. WinHlp32.exe is required in order to display 32-bit help
content files that have the ".hlp" file name extension.
However, the Windows Help program has not had a major update for many
releases and no longer meets Microsoft standards. Therefore, starting with
the Windows Vista operating system release, the Windows Help program will
not ship as a component of the Windows operating system. Also, third-party
programs that include .hlp files are prohibited from redistributing the
Windows Help program together with their products.
Users who want to view 32-bit .hlp files must download the program from the
Microsoft Download Center, and then install it on their computers. Users
who have not installed this program on their computer will be directed to a
help topic in the Windows Vista Help and Support application. To download
WinHlp32.exe, visit the following Microsoft Web site: