<div id='foo'>  
  То, что будет мигать  
  </div>

<script type='text/javascript'>  
  function startAnim(element, time) {  
  element.animTimer = setInterval(function () {  
  if (element.style.display == "none")  
  element.style.display = "";  
  else  
  element.style.display = "none";  
  }, time);  
  }  
  function stopAnim(element) {  
  clearInterval(element.animTimer);  
  }  
  startAnim(document.getElementById("foo"), 500);  
  document.getElementById("foo").onmouseover = function () {  
  stopAnim(this);  
  };  
  document.getElementById("foo").onmouseout = function () {  
  startAnim(this, 500);  
  };  
  </script>