centos4.4 Java(TM) SE Runtime Environment (build 1.6.0-b105)で
wget http://downloads.freenetproject.org/alpha/installer/new_installer.jar
java -jar new_installer.jar
を実行すると、下のように出るのですが何が原因ですか？

Exception in thread "main" java.lang.ExceptionInInitializerError
at com.birosoft.liquid.LiquidLookAndFeel.loadIconImmediately(LiquidLookAndFeel.java:708)
at com.birosoft.liquid.LiquidLookAndFeel.loadIcon(LiquidLookAndFeel.java:686)
at com.birosoft.liquid.LiquidLookAndFeel.initComponentDefaults(LiquidLookAndFeel.java:514)
at javax.swing.plaf.basic.BasicLookAndFeel.getDefaults(BasicLookAndFeel.java:130)
at javax.swing.UIManager.setLookAndFeel(UIManager.java:537)
at javax.swing.UIManager.setLookAndFeel(UIManager.java:581)
at com.izforge.izpack.installer.GUIInstaller.loadLookAndFeel(GUIInstaller.java:346)
at com.izforge.izpack.installer.GUIInstaller.<init>(GUIInstaller.java:116)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at java.lang.Class.newInstance0(Class.java:355)
at java.lang.Class.newInstance(Class.java:308)
at com.izforge.izpack.installer.Installer.main(Installer.java:62)
Caused by: java.awt.HeadlessException:
No X11 DISPLAY variable was set, but this program performed an operation which requires it.
at sun.java2d.HeadlessGraphicsEnvironment.getDefaultScreenDevice(HeadlessGraphicsEnvironment.java:64)
at com.birosoft.liquid.skin.SkinImageCache.<clinit>(SkinImageCache.java:41)
... 15 more