code: private static boolean isWindowsXPLafEnabled() {
          return IS_OS_WINDOWS
                  && Boolean.TRUE.equals(Toolkit.getDefaultToolkit().
                          getDesktopProperty("win.xpstyle.themeActive"))
                  && getSystemProperty("swing.noxp") == null;
      }
docs: Checks and answers whether the Windows XP style is enabled. This method is intended to be
  called only if a Windows look&feel is about to be installed or already active in the
  UIManager. The XP style of the Windows look&amp;feel is enabled by default on Windows XP
  platforms since the J2SE 1.4.2; it can be disabled either in the Windows desktop as well as
  in the Java runtime by setting a System property.<p>
  
  First checks the platform, platform version and Java version. Then checks whether the desktop
  property <tt>win.xpstyle.themeActive</tt>
  is set or not.
  
  @return true if the Windows XP style is enabled