If the user selects a mouse that has a wheel (such as Intellimouse or Logitech Mouseman+/Firstmouse+) the line: ZAxisMapping 4 5 (for 3.3.x) or Option "ZAxisMapping" "4 5" should be added to the pointer section so that the wheel will work properly.
Fixed in CVS, thanks.
*** Bug 10035 has been marked as a duplicate of this bug. ***