If I have 8.1, how do I add 7 as dual boot?

I may be in the wrong place - my wife says I'm ALWAYS in the wrong place - but at least I ask for directions. 1) Where is there another great thread that tells me how to add Win 7 Pro 64-bit as a dual boot if I am starting with Win 8 (or 8.1) Pro 64-bit already installed? (Maybe it's here, but on which of these 36 pages?) 2) Can I do that by adding a second hard drive instead of...