Force IE Compatitbility Mode
IE has a header for controlling this, X-UA-Compatible.  Normally, people set this to 'IE=edge,chrome=1' which disables compatibility mode and tries to force Google Chrome Frame.  If you want to emulate IE7, you can use 'EmulateIE7'.

In Drupal 7, it is best to use a hook_html_head_alter for this

function MYTHEME_html_head_alter(&amp;$head_elements) {
  $head_elements['MYTHEME_ie_compatability'] = array(
    '#type' =&gt; 'html_tag',
    '#tag' =&gt; 'meta',
    '#attributes' =&gt; array(
    'name' =&gt; 'X-UA-Compatible',
    'content' =&gt; 'EmulateIE7',
    ),
  );

  $head_elements['MYTHEME_ie_compatability']['#attached']['drupal_add_http_header'][] = 
    array('X-UA-Compatible', $head_elements['MYTHEME_ie_compatability']['#attributes']['content']);
}


This sets the &lt;meta&gt; in the &lt;head&gt; and also sets an HTTP header in the response.

In Drupal 6, you could use

function MYTHEME_preprocess_page(&amp;$variables) {
  drupal_set_header('X-UA-Compatible: EmulateIE7');
}


You can also do this via Apache (eg, in .htaccess) with

&lt;IfModule mod_headers.c&gt;
  Header set X-UA-Compatible EmulateIE7
&lt;/IfModule&gt;