function featuredtoRSS($content) {
	global $post;
	if( has_post_thumbnail( $post->ID ) ) {
		$content = '' . get_the_post_thumbnail(
		$post->ID, 'thumbnail',
		array ( 'style' => 'float:left; margin:0 15px 15px 0;') 
		). '' . $content;
	}
	return $content;
}
add_filter('the_excerpt_rss', 'featuredtoRSS');
add_filter('the_content_feed', 'featuredtoRSS');