[pauldodman]

You need to edit thickbox/thickbox_productpage.tpl

Here is a sample file - alter it to suit...

 
{if $images ne ""}
<div style="white-space:nowrap;color:#D90000;font-weight:bold;padding:2px;margin:10px 0 4px;">{$lng.lbl_detailed_images} &not;</div>
<table width="250"><tr>
{section name=image loop=$images}
<td>
{if $images[image].avail eq "Y"}
{if $images[image].tmbn_url} 
<a href="{$images[image].tmbn_url}" title="{$images[image].alt|escape}" class="thickbox" rel="lightbox_detailed"><img src="{$images[image].tmbn_url}" height="50" style="border:0;" alt="{$lng.lbl_click_to_enlarge|escape}" /> {if $images[image].alt|escape eq ""} {$lng.lbl_image} {math equation="value+1" value=$smarty.section.image.index}{/if}</a></div>
{else}
<a href="{$xcart_web_dir}/image.php?id={$images[image].imageid}&amp;type=D" title="{$images[image].alt|escape}" class="thickbox" rel="lightbox_detailed"><img src="{$SkinDir}/thickbox/files/zoom.gif" style="border:0;" alt="{$lng.lbl_click_to_enlarge|escape}" /> {$images[image].alt|escape}{if $images[image].alt|escape eq ""} {$lng.lbl_image} {math equation="value+1" value=$smarty.section.image.index}{/if}</a></div>
{/if}
{/if}
</td>
{/section}</tr>
</table>
{/if}