I don’t think a lot of people know this because I don’t quite see people using this commenting system or even embedding this into their new blogspot templates. Many people find Blogspot commenting style quite disturbing, including myself. This is because it involve loading popup, knowing that some blog will not allow you to comment if you do not own a blogger account, and sometimes captcha.
Jackbook has actually come out with a hack which could enable visitor to comment on the same page as the posting page.
It takes a while to look for the code, especially if you have a custom theme. Therefore remember to backup you theme.
Make sure you follow the instruction carefully. I would recommend you to copy the code in a text file and then recopy it back to your blogspot template.
Learn how to have WordPress Comment on Blogspot