WordPress has this very easy and straight forward logic when it comes to RTLing themes. It simply checks for the direction of the language you're using in your WP installation, if it happens to be 'rtl'(Arabic for example) it includes the stylesheet
rtl.css if it exists. This means that RTLing a WP theme is creating this
rtl.css file. A detailed tutorial is coming up soon about RTLing WP themes
rtl.css for you from your theme's
Check the RTLer out at the WordPress Plugin Directory.