Template question

I've just been tweaking the template code for simple stuff to widen the text areas for the main body and the sidebar, that all seems fine. My template skills are non-existent however, I only knew how to widen the columns because I looked over the code and picked out stuff to do with pixels and so on. What I want to do is add a horizontal break line after each post, so that the format would be something like

POST
LINE
POST
LINE
POST

and so on. Anybody know of any way to do that, or know where I should look for assistance?