conditional CSS

hi there.. need a little help..
i did a tutorial a learned that by including this code in the header.php file..

<?php if (is_page_template(‘page-inner.php’)) { ?>
<link rel=”stylesheet” href=”<?php bloginfo( ‘template_url’ ); ?>/css/page-inner.css” />
<?php } ?>

for example.. i can call a certain css file for pages.. i have been looking around the web for hours now and cant seem how to do this with single.php files. is this possible and if so how ?

i tried this and it IS NOT seeing the css file..

<?php if (is_single(‘ourclients’)) { ?>
<link rel=”stylesheet” href=”<?php bloginfo( ‘template_url’ ); ?>/css/page-inner.css” />
<?php } ?>

any help would be highly appreciated.

thanks in advance