Currently using GNU Emacs 23.1.1.
I've used xemacs since the late 90s and am only now switching to proper emacs.
If I had my xemacs window split into a top buffer and bottom buffer, I could move the keyboard focus between them with ctrl-tab. (I cannot remember if that's something I wrote myself 20+ years ago, or was a standard mapping, but checking my config files I don't think I wrote it myself.)
There are similar questions about rotating between buffers, but, I think, keeping the focus in the same sub-window. That's not my question, but just to be clear, the following is something I find very useful but isn't what this current question is asking. I probably have the wrong terminology, but the following code changes the buffer within the current sub-window. Instead I want to leave all the sub-windows looking at their current buffers, and instead move focus to the next sub-wind.
(defun switch-to-next-buffer () (interactive) (switch-to-buffer (other-buffer)))