Log in to your blogger account
Go to edit html
Make sure to back up your template first
Now find this
<data:post.body/>
Immediately before that paste this code
<!-- DIGG -->
<div style='float:right;'><script type='text/javascript'>digg_url = '<data:post.url/>';</script><script src='http://digg.com/tools/diggthis.js' type='text/javascript'/></div>
Then Save.
Add Digg Button
