Adding digg button in blogger is very simple,just do this small edit in your blog Template
1.Login to your blogger account using your id
2.In your dashboard click layout
3.In the layout click Edit Html in the tab bar
4.In the click Expand Widget.You may need to backup you template
5.In your template Use CTRL + F to open search,( many people don't know this).Search fro this code
<p><data:post.body/></p

Due to template differences,you may not find above code, then search for this
<data:post.body/>
6.Paste this on the line directly before it:
<div style='float:right; margin-left:10px;'><script type='text/javascript'>digg_url=&quot;<data:post.url/>&quot;;</script><script src='http://digg.com/tools/diggthis.js' type='text/javascript'/></div>

Save your template.The digg button will then be located on right top of every of your Post