You might get some tips form this thread..
<http://groups.google.com/group/comp.lang.java.gui/browse_frm/thread/b00948f2062e9338/efb8c4c90c30bd16?hl=en#efb8c4c90c30bd16>
..and there was some other project that produced a semi-transparent
Window for NetBeans (see linked screenshot)
<http://groups.google.com/group/comp.lang.java.advocacy/browse_frm/thread/378ce69e8ad8d315/4dfdec202e1bef74?hl=en#4dfdec202e1bef74>
HTH
Andrew T.