the problem there seems to be the adsense, making the height of the td tag higher then 94px which is the height of the image itself.
if you have access to the raw code of the page you can try this:
Code:
<!-- logo -->
<a name="top"></a>
<table border="0" width="100%" cellpadding="0" cellspacing="0" align="center" style="margin:0px; padding:0px;>
<tr>
<td align="left" valign="bottom"><a href="<A href="http://www.immigrant.ie/"><img">http://www.immigrant.ie/"><img src="http://www.irishwebmasterforum.com/images/misc/vbulletin3_logo_white.gif" border="0" alt="Immigrant.ie - Living and working in Ireland - Immigration" /></a>
</td>
<td align="center" valign="top">
<script type="text/javascript"><!--
google_ad_client = "pub-5837688024799585";
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "text_image";
//2007-03-20: Immi
google_ad_channel = "2321808298";
google_color_border = "e1e1e3";
google_color_bg = "e1e1e3";
google_color_link = "22229C";
google_color_text = "000000";
google_color_url = "22229C";
//-->
</script>
<script type="text/javascript"
src="[URL]http://pagead2.googlesyndication.com/pagead/show_ads.js[/URL]">
</script>
</td>
</tr>
</table>
<!-- /logo -->
or change it to divs.
Code:
<!-- logo -->
<a name="top"></a>
<div style="width:100%;height:94px;">
<div style="text-align:left; vertical-align:bottom; width:376px; height:94px;">
<a href="<A href="http://www.immigrant.ie/"><img">http://www.immigrant.ie/"><img src="http://www.irishwebmasterforum.com/images/misc/vbulletin3_logo_white.gif" border="0" alt="Immigrant.ie - Living and working in Ireland - Immigration" /></a>
</div>
<div style="width:100%; text-align:center; padding:0px; margin:0px;">
<script type="text/javascript"><!--
google_ad_client = "pub-5837688024799585";
google_ad_width = 728;
google_ad_height = 90;
google_ad_format = "728x90_as";
google_ad_type = "text_image";
//2007-03-20: Immi
google_ad_channel = "2321808298";
google_color_border = "e1e1e3";
google_color_bg = "e1e1e3";
google_color_link = "22229C";
google_color_text = "000000";
google_color_url = "22229C";
//-->
</script>
<script type="text/javascript"
src="[URL]http://pagead2.googlesyndication.com/pagead/show_ads.js[/URL]">
</script>
</div>
</div>
<!-- /logo -->
also right above the adsense code you have a <br /> tag.
Try removing that, cause it increases the height of the <td> tag by least 5px.