Download real-auto-save.el and put it in a folder where Emacs can find it. Add following lines to your .emacs initialization file:
(require 'real-auto-save)
(add-hook 'text-mode-hook 'turn-on-real-auto-save)
(add-hook 'muse-mode-hook 'turn-on-real-auto-save)
Auto save interval is 10 seconds by default. You can change it:
(setq real-auto-save-interval 5) ;; in seconds