Right got version 2.3 to work with an extra feature to show the full size image if you want it: 

Edit the file: editor/filemanager/browser/default/frmresourceslist.html  

First off paste the following code at the top, just within the 
<script type="text/javascript"> 
 
###START PASTE### 
function h2oDisplayNormal(h2oObj,h2oID) { 
var h2oImgStart='<img src="'; 
var h2oImgEnd='" border="0" />'; 
var h2oMyOutput=document.getElementById("h2o_"+h2oID); 
h2oMyOutput.style.display="block"; 
h2oMyOutput.innerHTML=h2oImgStart+h2oObj+h2oImgEnd; 
} 
function h2oDisplayNone(h2oObj) { 
var h2oMyOutput=document.getElementById("h2o_"+h2oObj); 
h2oMyOutput.style.display="none"; 
h2oMyOutput.innerHTML="";  
} 
### END PASTE ###
 
Then locate this line: 
 
oListManager.GetFileRowHtml = function( fileName, fileUrl, fileSize ) 
 
Comment out: 

/*return '<tr>' + 
'<td width="16">' + 
sLink +  
'<img alt="" src="images/icons/' + sIcon + '.gif" width="16" height="16" border="0"></a>' + 
'</td><td>&nbsp;' + 
sLink +  
fileName +  
'</a>' + 
'</td><td align="right" nowrap>&nbsp;' + 
fileSize +  
' KB' + 
'</td></tr>' ;*/ 
 
Then paste the following: 
/*================================================== 
Modification to display thumb nails  
Modifed date: 20/07/2006 
Modified by: http://www.h2odevelopments.co.uk 
==================================================*/ 
var imgH="52"; 
var imgW="52"; 
var h2oOutput=""; 
h2oOutput='<tr><td width="16">'+sLink+'<img alt="'+sIcon+'" src="images/icons/'+sIcon+'.gif" width="16" height="16" border="0"/></a></td>'; 
h2oOutput+='<td nowarp colspan="2">&nbsp;'+sLink; 
if(sIcon=="gif" || sIcon=="jpg" || sIcon=="png") { 
 
h2oOutput+='&nbsp;' + sLink + '<img src="'+fileUrl+'" alt="'+fileName+'" height="'+imgH+'" width="'+imgW+'" border="0"'; 
 
//=== Start of remove if you don't want to display full image on rollover 
var h2oFunc='h2oDisplayNormal(this.src,&#39;'+fileName+'&#39;)'; 
h2oOutput+=' onmouseover="'+h2oFunc+'"'; 
h2oOutput+=' onmouseout="h2oDisplayNone(&#39;'+fileName+'&#39;)"'; 
//=== End of remove if you don't want to display full image on rollover 
 
h2oOutput+=' /></a> ('+fileName+')'; 
h2oOutput+='<div id="h2o_'+fileName+'" style="display: none; border: 1px solid #ccc;padding: 2px;"></div>'; 
 
} else { 
h2oOutput+= '&nbsp;' + sLink + fileName + '</a>'; 
} 
h2oOutput+='</td><td align="right" nowrap>&nbsp;' +fileSize+' KB</td></tr>'; 
return h2oOutput; 
/*================================================== 
End of modifications 
==================================================*/