If it's a VBA question, I just open a code window and type my search term(s) into the Help window. But you're right, there doesn't seem to be any mechanism for searching all the associated help files. If you're in the main Access window, your search results will be entirely different from those you will get if you look for help while in the VBE, which will be different from the results you will get while in the VBA Object Browser. Not a very intuitive arrangement.
Ken S.