The IE7 compatibility tag – Force IE8 to use the IE7 rendering mode

If your site is not rendering properly in IE8, you can force IE8 to use the IE7 rendering mode with the following meta tag:
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7">

You also transmit this information in the header of the web page response. One way to do that quickly is via a .htaccess file with the following line:
Header set X-UA-Compatible IE=EmulateIE7

You can read more information about IE8 and IE7 compatibility over on MSDN.