Retreive template package root folder name using Jahia API

Hi,
 
  First time templating and programming with Jahia API and I was
wondering how can I dynamicaly retreive the complete path name to a
template.
 
With an instance of a JahiaSite object, I can find many usefull
information (servername, template folder, site key, etc...) but I can't
find a way to get the "root-folder" name for a template package (the one
that's define inside template.xml). For sure, I can hardcode the path
and it will be exact 98% of the time but I don't like this way of
programming :) 
 
I have found a class that may be usefull but I can't figure out how to
use it (JahiaTemplatesPackage).
 
Any help appreciated.
 
Pascal