How to apply category to page

change this:

if (is_page() ) {
$category = get_post_meta($posts[0]->ID, 'category', true);
}

to:

$category = 'uncategorised';

(make sure this is the spelling you want – the default category is spelled with a z)

be aware that PageOfPosts is written for the kubrick theme, and that you need to adjust the html structure to suit your existing theme.