How do I get the Mac Look and Feel on a Mac running MRJ?

If you are running MRJ, then you are not using Mac OS X and so you will not be getting the Aqua Look and Feel. The latest version of the MRJ (2.2.3 as of September 2000) corresponds to JDK 1.1.8. This supports Swing as a separate download. The Swing team did produce their own Mac Look and Feel. For a more "Mac" like version, take a look at the work of Luca Lutterotti and others at Luca's site.