With the release of Windows Vista, the windows help program (WinHlp32.exe) is no longer included. So when summoning the help of some older programs (“.hlp” files) you get a nice error message, but no help.
Shortly after the initial release of Windows Vista, Microsoft put the old WinHlp32.exe online for download in different language versions for both 32-bit and 64-bit versions of Vista.
The overview article is located at http://support.microsoft.com/kb/917607. A download link is also included in that article.