Code:
mkdir templates_c; chmod 777; chown nobody.nobody;
tempaltes_c/ is created upon installation however all subdirs are created from the actually Smarty.class template engine, hence the reason chmod 777 and change owner nobody. This way your webserver can write to the directory. If your running apache from another user other than nobody then you'll need to change it to the same permissions as your webserver is running.
http://smarty.php.net/