First, type your blog post and publish it. After that, submit your post to INNIT and you'll get the URL for the post in INNIT.
You can obtain the INNIT URL link from the address bar above right after you submit your post.
Next, put this code in the HTML section of your blog post.
|<a href="INNIT URL" target="_blank"><img src="http://innit.nuffnang.com/images/button_nangit_hover.gif"/></a>|
Just replace the INNIT URL with your URL and it's done! =)