Merhaba;
denemedim yedek alarak yapsan iyi edersin
Bunu bulup

// Show the post itself, finally!
		echo '
								</td>
							</tr></table>
							<hr width="100%" size="1" class="hrcolor" />
							<div class="post"', $message['can_modify'] ? ' id="msg_' . $message['id'] . '"' : '', '>', $message['body'], '</div>', $message['can_modify'] ? '
							<img src="' . $settings['images_url'] . '/icons/modify_inline.gif" alt="" align="right" id="modify_button_' . $message['id'] . '" style="cursor: pointer; display: none;" onclick="modify_msg(\'' . $message['id'] . '\', \'' . $context['session_id'] . '\')" />' : '' , '
						</td>
					</tr>';

Bunla değiştir

// Show the post itself, finally!
		echo '
								</td>
							</tr></table>
							<hr width="100%" size="1" class="hrcolor" />
														<table width="100%"  border="0">
														<td  valign="top" width="100%" height="100%">';
echo'

							<div class="post"', $message['can_modify'] ? ' id="msg_' . $message['id'] . '"' : '', '>', $message['body'], '</div></td>';
								if ($message['id'] == $context['first_message'])
echo '
<td  valign="top" width="250px" height="100%">
Reklam kodun
</td></table> ';
echo'
', $message['can_modify'] ? '
							<img src="' . $settings['images_url'] . '/icons/modify_inline.gif" alt="" align="right" id="modify_button_' . $message['id'] . '" style="cursor: pointer; display: none;" onclick="modify_msg(\'' . $message['id'] . '\', \'' . $context['session_id'] . '\')" />' : '' , '
						</td>
					</tr>';

Burda 250x250 adrense koduna göre yaptım...Genişliğine göre ayarlarsın width="250px" kodunu umarım olur...