So you have a great site, but does not render well in IE 8.

If it then works in compatibility mode, you need to make changes to your site.
If you need to make site wide changes the best way wold be to make an addition to your HTACCSSS file.

Add this to your htaccess

<FilesMatch ".(php)$">
Header set X-UA-Compatible "IE=7"
</FilesMatch>

or

<FilesMatch ".(php)$">
Header set X-UA-Compatible "IE=EmulateIE7"
</FilesMatch>

the first runs in Quirks mode, the second emulates

If you want to effect a single page only add this line at the top of your file, in the opening <?php tag
  if (strpos($_SERVER['HTTP_USER_AGENT'],"MSIE 8")) {header("X-UA-Compatible: IE=7");}

  if (strpos($_SERVER['HTTP_USER_AGENT'],"MSIE 8")) {header("X-UA-Compatible: IE=EmulateIE7");}

again the differences are Quirks and Emulate mode.

You may find you need to add a style definition to your <div id=" tags as this will effect your stylesheet output.

Here is a link that explains to you the differences