In higher resolution there will be more space and in 800x600 you visitors will not notice that cause the Admin button will not be there .. anyhow look in index.template.php look for:
<td width="10%" style="background-image: url(', $settings['images_url'], '/re_top_6.gif);"></td>
<td width="0%"><img src="', $settings['images_url'], '/re_top_5.gif" alt="" /></td>
<td width="60%" style="background-image: url(', $settings['images_url'], '/re_top_4.gif);" align="left">';
and change the percentage of 10% to 1% and 60% to 69% and hopefully this will allow for more space.