the filenames are very descriptive
Oh yeah, that's true :) We thought that will be enough, but if you are having troubles with some template, just ask here, and we'll explain.
Alternatively, it is possible to modify bb_functions.php file - function makeUp(). Where it says
replace it to:
if (substr($name,0,5)!='email') return "".$tpl.""; else return $tpl;
Then if you view the source of the whole page (while working on the layout of your forums) you will see the commenting tags meaning which template is used via parsing.
Please note this approach is for debugging purposes only. It produces a wrong HTML and can't be used (needs to be disabled) on the production page.