dashboard > design > edit HTML *tick expand widget templates
press Ctrl + C and find this code
data:post.body
put this facebook like button code under that code
<em><iframe allowTransparency='true' expr:src='"http://www.facebook.com/plugins/like.php?href=" + data:post.url + "&layout=standard&show-faces=true&width=530&height=60&action=like&colorscheme=light"' frameborder='0' scrolling='no' style='border:none; overflow:hidden; width:530px; height:60px'/></em>
preview first, the save :))