If you want to decorate, you might have to be more
specific, just some of my thoughts about Swing: My
guess (this might me completely wrong) is that you
have gotten into the standard motif Swing, it's ugly.
It's like regular Unix CDE and a bit worse. Please
note that where the mac (with bulit-in java) probably
will show it's default beatyfully designed Mac OS X in
JVM, windows will not, it will show standard swing  by
default.

By using this import

import javax.swing.UIManager;

and the code  below, you will change the look and feel
to the current Windows settings on your PC (or mac
will show it's native OS look and feel of course).

// This will look like Windows under Windows

UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());

There are some other UIManager alternatives that might
work independently of the OS, check the SDK. Or
rewrite new swing windows and other components, just
extend the classes that you want to use as a base
class, people have done that, there is also usually a
fee involved in order to get the code.