onMouseMove = function(event)
  {
    m_x = (document.all) ? window.event.clientX : event.pageX;
    m_y = (document.all) ? window.event.clientY : event.pageY;
    
    if (m_element !== null)
    {
      Element.setStyle(m_element, {
        top : (m_y - m_top ) + "px",
        left: (m_x - m_left) + "px"
      });
    }
  }
Callback. Wird beim Bewegen der Maus aufgerufen