Basically, I want to give my articles and blog entries a different class on the body so I can style them independently.

I am given to understand that the best way to do this is with creating custom tpl files

I'm working in a custom built theme that is pretty much running just on a page.tpl.php and a stylesheet.

How would I do this easily in Drupal 7? I tried this method for drupal 6 but it didn't seem to work.