<script type="text/javascript">
    $(document).ready(function() {
            $("div.profCores ul li a").hover(function() {

            var largePath = $(this).attr("href");
            var largeAlt = $(this).attr("title");

            $("#largeImg").attr({ src: largePath, alt: largeAlt });

            return false;
        });

    });
</script>

<img src="img/imgBlank.gif" alt="Santher" id="largeImg" />
<div class="profCores">
<strong>Cores Dispon�­veis:</strong>
  <ul>
    <li><a href="img/imgBlank2.gif" class="btnCor1" onclick="javascript:mudaImg('abrirFoto','img/imgBlank2.gif');">cor 1</a></li>
    <li><a href="img/imgBlank3.gif" class="btnCor2">cor 2</a></li>
    <li><a href="img/imgBlank4.gif" class="btnCor3">cor 3</a></li>
    <li><a href="img/imgBlank5.gif" class="btnCor4">cor 4</a></li>
    <li><a href="img/imgBlank6.gif" class="btnCor5">cor 5</a></li>
  </ul>
</div>

http://www.lordfury.net/AssociatedContent/Associated%20Content%20Uploads/jQueryRound2/ImageReplacementGal.html

Alterar imagem - hover

script, jquery

jQuery