How To Add Recent Comment Post Script For Your Blogger
First all code bellow

<style type="text/css">
ul.md_recent_comments{list-style:none;margin:0;padding:0;}
.md_recent_comments li{background:none !important;margin:0 0 6px !important;padding:0 0 6px 0 !important;display:block;clear:both;overflow:hidden;list-style:none;}
.md_recent_comments li .avatarImage{padding:3px;background:#fefefe;-webkit-box-shadow:0 1px 1px #ccc;-moz-box-shadow:0 1px 1px #ccc;box-shadow:0 1px 1px #ccc;float:left;margin:0 6px 0 0;position:relative;overflow:hidden;}
.avatarRound{-webkit-border-radius:100px;-moz-border-radius:100px;border-radius:100px;}
.md_recent_comments li img{padding:0px;position:relative;overflow:hidden;display:block;}
.md_recent_comments li span{margin-top:4px;color: #666;display: block;font-size: 12px;font-style: italic;line-height: 1.4;}
</style>
<script type="text/javascript">
//<![CDATA[
    // Recent Comments Settings
    var
 numComments  = 5,
 showAvatar  = true,
 avatarSize  = 50,
 roundAvatar = true,
 characters  = 30,
 showMorelink = false,
 moreLinktext = "More &#187;",
 defaultAvatar  = "http://www.gravatar.com/avatar/?d=mm",
 hideCredits = true;
//]]>
</script>
<script type="text/javascript" src="http://makingdifferent.github.com/blogger-widgets/md-recent-comments-gravatar.js"></script>
<script type="text/javascript" src="http://www.yourdomainblogspot.com/feeds/comments/default?alt=json&callback=md_recent_comments&max-results=5"></script>

Than Paste in to your Widget for Html Script

Make sure to change your  yourdomain to your own domain :D

than save and reload the page

done ...