I am trying to add some buttons to a chess board, but for some reason the don't appear on the board.

Consider the following code:

Code:
public class Board {
	
	public static void main(String[] args) {
		Board nb=new Board(new Display());
		nb.run();
		
	}
	
	
	private Shell shell;
	private Display display;
	private IModel model;
	
	public Board(Display main_display) {
		display=main_display;
		shell=new Shell(display,SWT.DIALOG_TRIM);
		shell.setText("Board");
		Image background=new Image(display, "chess_board.jpg");
		shell.setBackgroundImage(background);
		shell.setBackgroundMode(SWT.INHERIT_DEFAULT);
		
		Composite co=new Composite(shell, SWT.NO_BACKGROUND);
		co.setBounds(background.getBounds());
		co.setLayout(new GridLayout(8,true));
		
		Button b1=new Button(co, SWT.PUSH);
		b1.setText("Test Button");		

		shell.pack();
	}
	

	public void run() {
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch()) 
				display.sleep();
		}
		display.dispose();
	}
}
where I'm trying to add one button.
The b1 button won't appear on the board.
does anyone know what is it all about?

thanks.