Using a double boiler, put water in the bottom and heat and boil. In the top of the boiler, put 3 cups of water. When both start boiling, put the top pan on the bottom pan, and add the rice to the boiling water in the top pan.
When boiling again, put cover on and low boil for 40 minutes. You may have to check half way through cooking and add more boiling water to the bottom pan. After the 40 minutes, add more boiling water to the bottom. Add the margerine, and the condensed milk to the rice. Stir until well blended. Cook 20 minutes longer uncovered till thick. Take off heat and add vanilla and raisens if desired.