Auto Post Thumbnail Wordpress Plugin For BBCode

Anybody here can help me customize the Auto Post Thumbnail for BBCode: http://www.sanisoft.com/blog/2010/04/19/wordpress-plugin-automatic-post-thumbnail/
I think here is the content for it, it's getting the thumbnail by html now:

// Get all images from post's body
preg_match_all('/<\s*img [^\>]*src\s*=\s*[\""\']?([^\""\'>]*)/i', $post[0]->post_content, $matches);

PHP:

Thanks!