If you have an old Windows program that uses 32-bit .hlp files, you already know those files don’t open in Windows Vista. The solution? Download WinHlp32.exe for Windows Vista. Microsoft clearly doesn’t recommend that you do so, as this paragraph on the download page suggests:
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.
But if you need it, hey, go ahead and install it.
Ed Bott (@ wordpress.com) 
Brillant. We happen to have a piece of software that autoruns a help program at startup unless you uncheck the box. Works fine in XP, of course bombs out on Vista. Doesn’t affect the software itself, just bombs a little on restart. This will save us some time. Thanks, Ed.
Shouldn’t most people have moved to *.chm or HTML help files by now?
Anthony, you’re right, most developers moved to more modern Help file formats long ago. But some people have come to depend on old (pre-2000) applications that perform a specialized task and can’t be replaced easily or cheaply. This workaround is for them.