To do some basic customisation just requires a little HTML knowledge as the .tpl files are mainly html but with some extra logic that html cannot do.
If you work with dreamweaver mx - i would suggest that simple look and feel stuff can be done in that but most of the really technical stuff will require being able to edit html/smarty directly.
Smarty can be read about at
http://smarty.php.net
I am sure that it will not take you long to learn a little about how it works and make your own mods.