Give this a whirl. Looked like the bottom row was the problem and the centering coding:
PHP Code:
<table align="center" border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td background="forums/images/myimages/nav_r_01.jpg" align="right"><strong><font color="#FFFFFF" size="3">On
This Date</font><img src="forums/images/myimages/nav_right_mid_01.jpg" align="absmiddle"></strong></td>
</tr>
<tr>
<td><img src="forums/images/myimages/nav_r_03.jpg"></td>
</tr>
<tr>
<td align="center" valign="top" background="forums/images/myimages/nav_r_04.jpg"><font color="#20438A">
<script src="forums/external.php?type=js&forumids=23" type="text/javascript"></script>
<script type="text/javascript">
<!--
for (i = 0; i < 1; i++)
{
document.writeln(""+threads[i].title+"");
}
//-->
</script>
</font></tr>
</table>
That centers the the bottom scripts which I think is what you were having the problem with? If not, try a "align="center" in front of the valign in that line of your original code?