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Upload delay-print-css to the /wp-content/plugins/ directory of your install.

Activate the plugin through the 'Plugins' menu in WordPress

In your theme or plugin, use wp_register_style and/or wp_enqueue_style to load your CSS. This requires you to remove any html tags you have in your theme and add the following code to your functions.php file:

function mytheme_enqueue_css(){
  if (!is_admin()){
    wp_enqueue_style (
      'mytheme-print', /* handle */
      '/path-to/print.css', /* source */
      null, /* no requirements */
      '1.0', /* version */
      'print' /* media type */
    );
  }
}
add_action('wp_print_styles', 'mytheme_enqueue_css');

To wrap your stylesheet in conditional tags, add the following below the wp_enqueue_style call in your new function

global $wp_styles;
$wp_styles->registered['mytheme-print']->extra['conditional'] = 'IE 6'