I haven't looked into it but I strongly suspect that the problem is within the "moveIt" method.
It uses "event", which unless it is a property of window (i.e. window.event) it is not in scope.
I believe in IE, window.event is defined, whereas in all other normal browsers (:p) it is not. Instead the event is passed to the listener. Therefore, to get that script to work moveIt should take event as a parameter (and may also have to use different properties of it, I can't remember exactly...)