You don't need to do anything fancy to show someones gravatar, just find it somewhere on the web and copy the URL for it.
You would do it something like this:
Code:
<div class="guestposter">
bla bla bla discussion about me ...
a href="http://pixopoint.com/" rel="external nofollow" title="Ryan"><img alt='Ryan' src='http://www.gravatar.com/avatar/a084125c824d274ff40cb834cf9f544a?s=80&d=identicon&r=R' height='80' width='80' /></a>
</div>
And you would have CSS to go with it:
Code:
.guestposter {background:grey;border:1px solid #666;}
.guestposter img {float:right;border:1px solid #ccc;}