HTML5, WP, functions.php: HTML5 Shim in functions.php

index.php

// add ie conditional html5 shim to header
function add_ie_html5_shim () {
	global $is_IE;
	if ($is_IE)
   	echo '<!--[if lt IE 9]>';
    	echo '<script src="http://html5shim.googlecode.com/svn/trunk/html5.js"></script>';
    	echo '<![endif]-->';
}
add_action('wp_head', 'add_ie_html5_shim');

// From http://css-tricks.com/snippets/wordpress/html5-shim-in-functions-php/