http://www.sita.co.za/FOSS/FOSS1.html
A policy alone doesn't seem to help, as can be seen here: http://www.itweb.co.za/index.php?option=com_content&view=art...
Legislation might be a better approach. I couldn't find the exact numbers now, but a country like RSA sends around 1 billion US out of the country for software licenses yearly.