amMap has a setting, <mouse_wheel_enabled> which, if set to "true", allows zooming the map with mouse wheel. However in some cases this is not working with some browsers. A solution would be to use JavaScript functions flashMovie.zoomIn() and flashMovie.zoomOut() - you can register events of mouse wheel with JavaScript and call these functions. Here is the sample code:

<code javascript>
<script type="text/javascript">

   function handle(delta) {
       if (delta < 0)
           flashMovie.zoomOut();
       else
       flashMovie.zoomIn();
   }

   function wheel(event){
       var delta = 0;
       if (!event) event = window.event;
       if (event.wheelDelta) {
           delta = event.wheelDelta/120;
           if (window.opera) delta = -delta;
       } else if (event.detail) {
           delta = -event.detail/3;
       }
       if (delta)
           handle(delta);
           if (event.preventDefault)
                   event.preventDefault();
           event.returnValue = false;
   }

   if (window.addEventListener)
       window.addEventListener('DOMMouseScroll', wheel, false);
   window.onmousewheel = document.onmousewheel = wheel;


   function amMapCompleted(map_id){
     flashMovie = document.getElementById(map_id);
   }

 </script>
</code>