linebreak after the content?

Hell0 i have been trying to figure out how i can put a picture after the last letters in a post.I can get it to show up under the facebook like buttons but i also want a line break over that button

heres the Index.php where div class=”post_line” is conected to an image in the css file,Why cant i just put <div class=”post_line”></div> below <div class=”post_content”> ?? it then shows a dubble line over the first at the top.
here is a picture of what i mean.

http://i55.tinypic.com/2wf07wj.jpg

<div class="post_line"></div>
                    <div class="post_content">
                    <?php the_content('Read more...'); ?>
                     <?php wp_link_pages('before=<b>Pages:</b><br/><div id="page-links">&after=</div>'); ?>
                    </div>
                    <div class="post_line"></div>
                    <div class="post_data">

Hope someone can help me