I have only tested this on linux so far.

Building

1. checkout SwingWT and apply the patch which is in
   AWTonSWT The only part of this patch you need is the
   changes to SWTGraphics2DRenderer.

Running

1. Add AWTonSWT and SwingWT (and its dependencies) to
   the boot classpath.
2. It seems the java.native.lib property isn't used by the
   bootclassloader, so you need to copy the swt native libraries into

   jdk/jre/lib/[platform]/

3. define the following properties when you run java
   -Dawt.toolkit=awtonswt.SWTToolkit
   -Djava.awt.graphicsenv=awtonswt.SWTGraphicsEnvironment
   -Djava2d.font.usePlatformFont=false
   -Djava.awt.fonts=/opt/sun-jdk-1.4.2.10/jre/lib/fonts

Running on OSX

Coming Soon.

It runs on my 10.3 computer. But the necessary changes aren't checked into CVS.
It needs a custom libawt.jnilib, and a few tweaks to the SwingWT code, and a Loader class that starts up some necessary OSX things before running your main method.

Currently the aqua look and feel doesn't work.