Microsoft decided not to ship Windows 7 and Vista with WinHlp32.exe which allows legacy .hlp files to be accessed.
It is available as a download from Microsoft from this location http://support.microsoft.com/kb/917607 and it is quick and easy to install. It is an annoyance, but easily fixed.
Best regards
Rob-T
The NWC2 help system uses HtmlHelp, so this topic only applies to the older NWC Version 1.75.