Adding CSS files in sub-themes

I need to add two css files, a front-page.css for the frontpage and an admin.css for all the admin pages.

I had a look to the following code I found in the template.php file:

<php?
// Example: optionally add a fixed width CSS file.
if (theme_get_setting('STARTERKIT_fixed')) {
  drupal_add_css(path_to_theme() . '/layout-fixed.css', 'theme', 'all');
}
?>

but I couldn't figure out how to use it to add the front-page.css and the admin.css files.

So I used the following snippet which works pretty well (see http://drupal.org/node/225868):

<?php
function mytheme_preprocess_page(&$variables) {
  $front_style = path_to_theme() .'/front-page.css';
  $path_style = path_to_theme() .'/path-'. arg(0) .'.css';

  if (file_exists($front_style) && $variables['is_front']) {
    $include_style = $front_style;
  }
  elseif (file_exists($path_style)) {
    $include_style = $path_style;
  }

  if (isset($include_style)) {
    drupal_add_css($include_style, 'theme', 'all', FALSE);
    $variables['styles'] = drupal_get_css();
  }
}
?>

BUT... the frontpage and all the admin pages do not read the ie.css file. While in all other pages I can see in the page source the code

<!--[if IE]>
<link type="text/css" rel="stylesheet" media="all" href="/sites/all/themes/mytheme/ie.css?M" />
<![endif]-->

on frontpage and on admin pages it doesn't show up and, of course, IE6 & 7 do not read it. I can bypass the problem by hacking directly the css.files (layout.css ecc) but I would like to find a standard solution which uses ie.css.

Any idea of how I can handle?

Thank you !