Why won't Help (.hlp) files view properly with Windows Vista?
In order to view 32-bit Help (.hlp) files with Windows® Vista, you must download the WinHlp32.exe Help program from the Microsoft web site at http://go.microsoft.com/fwlink/?LinkID=82148.
The Windows Help program (WinHlp32.exe) has been included with Microsoft Windows operating systems starting with Windows version 3.1. However, the Windows Help program is not provided with Windows Vista by Microsoft, and third-party programs that include .hlp files are not allowed to distribute this program. Therefore, in order to view .hlp files on Windows Vista, you must download the Windows Help program from Microsoft. Note that you need only do this once for all applications that require it.
Note: Windows Vista does support Windows HTML Help (.chm) files without any action on your part.