Look at the page source - it's all there. They are using images in the css to do it. For instance, if you look at the page source for the bottom of the post, you'll see this:
HTML Code:
<div class="bottomquote"><div class="i"></div></div>
Then look at the css for that, and you see this:
HTML Code:
div.bottomquote{background: #FFFFFF url(/alphaimages/postbit/bottomquote.gif) no-repeat bottom left;height: 14px;margin-bottom: 20px;}div.bottomquote div.i{background: url(/alphaimages/postbit/bottomquote_right.gif) no-repeat bottom right;height: 14px;}
/* ***** rounded corners ***** */