I am not aware of any such guide, but one would certainly be useful. Can I just throw in a recommendation for an excellent tool for writing end-user docs (help, HTML, PDFs etc.), which is HelpNDoc. I use it on all my projects, and it's free for non-commercial use, and pretty cheap for commercial use.
Forget RoboHelp. It's expensive and, IMO, overly complicated for what you want to do.
For your purposes--a basic help system, relatively simple interface, try HelpnDoc. http://www.helpndoc.com/ Free, and pretty versatile.