The following test prints the insets for all screens on the system.  On RedHat 7.2 running GNOME/sawfish, getScreenInsets() does not recognize the GNOME taskbar - the insets are always 0,0,0,0.  I tried 1.4, 1.4.1b19 and 1.4.2b01.

// Print insets for all screens
import java.awt.*;

public class ScreenInsets {
    public static void main(String[] args) {
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice[] gds = ge.getScreenDevices();
        for (int i = 0; i < gds.length; i++) {
            GraphicsConfiguration gc = gds[i].getDefaultConfiguration();
            System.out.println(gc + ", insets: " + Toolkit.getDefaultToolkit().getScreenInsets(gc));
        }
    }
}