Change Image On Mouse Over With JavaScript

<script language="javascript" type="text/javascript">
    function changeImgOver()
    {
        document.getElementById("facebook").src = "images/facebook_over.png";   
    }
   
    function changeImgOut()
    {
        document.getElementById("facebook").src = "images/facebook_img.png";   
    }
</script>

 /*   Image code */

<div class="facebook_img" onmouseout="changeImgOut();" onmouseover="changeImgOver();"><a href="#"><img id="facebook" src="images/facebook_img.png" alt="facebook" border="0" /></a></div>