Use a JWindow bean
to add a window without a title bar, sizing borders, and sizing
buttons. This bean is suitable for a splash window that your
application displays briefly at startup.
The JWindow bean provides a content pane in which to place other components. The content pane provides logical separation of the window from its child components. With the exception of a JMenuBar, user interface components are added to the content pane, which completely covers the JWindow bean in the Visual Composition Editor. The JWindow bean can be accessed from the Beans List. The default content pane, a JWindowContentPane, is represented in the Beans List as the child of the JWindow bean. You can delete the default content pane and replace it with another container component.
Use a Window bean, rather than a JWindow bean, if you want to use AWT components in the window.
Composing a window
Sun's JWindow bean documentation
Window beans
Beans for visual composition