Hello !
Il suffit d'accéder à ton image comme tu accèdes à ton div, par son id :
<html>
<head>
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Nouvelle page 1</title>
</head>
<script language="javascript">
function hideShow(id_div)
{
var img = "image";
img += id_div ;
if (document.getElementById(id_div).style.display=='block')
{
document.getElementById(id_div).style.display='none'
document.getElementById(img).src='../img/arrow_down.gif'
}
else
{
document.getElementById(id_div).style.display='block'
document.getElementById(img).src='../img/arrow_up.gif'
}
}
</script>
<body>
<a href="#">
<img src="../img/arrow_up.gif" name="image1" border="0" id="image1" onClick="hideShow(1)">
</a>
<div id="1" style="display:block ">
<table width="500" border="1" id="1">
<tr><th>test</th></tr>
<tr><td>page 1</td></tr>
<tr><td>page 2</td></tr>
</table>
</div>
<hr>
<a href="#">
<img src="../img/arrow_up.gif" name="image2" border="0" id="image2" onClick="hideShow(2)">
</a>
<div id="2" style="display:block ">
<table width="500" border="1" id="2">
<tr><th>test</th></tr>
<tr><td>page 1</td></tr>
<tr><td>page 2</td></tr>
</table>
</div>
</body>
</html>
Et voilà. Bonne continuation.