To use the LAF used by the native OS:
UIManager.setLookAndFeel(UIManager.getSystemLookAn dFeelClassName());
Code from Sun's Swing Tutorial, look
here for more detail.
Yes, this is Swing only, not AWT. And as a user of both Windows and Linux systems: while AWT bore a passing resemblance to GTK a few years ago, GTK looks very different these days. Also, AWT doesn't have to be used on Unix/Linux, those systems will run Swing applications just fine. (I am a Swing developer, and use Ubuntu 8.04

)