Okay ich hatte Zeit 
:
HTML
<html>
<head>
<SCRIPT LANGUAGE="JavaScript">
<!--
function doPic(imgName) {
document.getElementById('mainpic').src = imgName;
}
//-->
</script>
</head>
<body>
<table width="100%" border=0 cellspacing=0 cellpadding=0 style="text-align:center;">
<tr>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
</tr>
<tr>
<td colspan=4 align=center><img id="mainpic" src="" border=0></td>
</tr>
<tr>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
<td><a href="javascript:doPic('');"><img src="" width=90 height=60 border=0></a></td>
</tr></table>
</body>
</html>Funktioniert ohne Probleme (musst natürlich noch deine Bildnamen einfügen).