To enable your scrollwheel for emacs:

;;; scrollwheel support
(defun scroll-up-half ()
  "Scroll up half a page."
  (interactive)
  (scroll-up (/ (window-height) 2))
  )
      
(defun scroll-down-half ()
  "Scroll down half a page."
  (interactive)
  (scroll-down (/ (window-height) 2))
  )
(global-set-key [(mouse-5)] 'scroll-up-half)
(global-set-key [(mouse-4)] 'scroll-down-half)

(nescivi, may 2007)