There seems to be some confusion surrounding this subject, so I decided to do some research and post my results in the forums in an attempt to eliminate (or at least remove much of) the confusion.
Making RTL sites with Joomla!
If you want to use your site's joomla templates in Hebrew and Arabic, they must be designed for right-to-left writing. Some of the templates included in Joomla! 1.5 are "ambi-languagestrous", meaning they’ll detect if the text direction is RTL and deploy a special CSS file which overrides the usual (LTR) settings.