Windows Help program (WinHlp32.exe) is no longer included with Windows. If you go to Microsoft knowledge base article 917607 you will find that
“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 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 Microsoft Windows Vista and the Microsoft Windows Server Code Name “Longhorn” operating system releases, the Windows Help program will not ship as a component of Windows. 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. The download for Windows Help is still in development. It will be available in time for the consumer release of Windows Vista scheduled for early 2007.”
That’s right, Vista no longer supports Winhelp, the old help engine little changed from Windows 3.1 days. To be honest it was dated, but it was fast and effective and some people never took to .chm. There are literally thousands of line-of-business applications in use today that use this type of help file. And the source code from a large number of these applications have been long been lost. Apparently it is not quite as bad as it first appears. Microsoft is going to offer winhlp32.exe for download.
In the meantime, you can do what I did, which is to copy winhlp32.exe from Windows XP. It works on RC2 and higher versions. Remember that there are 2 copies of Winhlp32.exe files in Windows XP Copy the one in the Windows folder and not the one in the system32 folder. After copying file to your Vista Windows folder, right click on any *.hlp file and choose Open With menu. Choose the newly copied WinHlp32.exe as the default program to open with. Now hlp file will be associated with WinHlp32.exe and not the Windows 32 Help Stub they were originally associated with. You can also Convert WinHelp (HLP) to HTMLHelp (CHM).
Update: Microsoft has now released winhlp32.exe for Windows Vista