I just found this out today. If you have Books Online installed on your system, did you know you can look at the local content in a regular old web browser? At the top of a Books Online topic, you’ll see a URL bar. The URL starts with ms-help://, which is really just another protocol pointing to the installed location of Books Online on your computer. Copy that URL and paste it into a browser, and voila, there it is!
Of course, you can always just go to the web for Books Online and get the content there.