When you say Blogger - you're talking about the Google Application right?
From what I've read there's no EASY way to add in a newsletter field. You can edit the template and insert HTML code if you wanted - that's probably the best bet.
Others say to create a google groups, then link off to that to collect the information - but it seems that Blogger has restricted the ability to put a form on your site with just a click of a button.
Wordpress on the other hand- VERY EASY