Okay, JDK (at least one from SUN) will allow you to create an embedded frame, that you can pass your window handle to. So,
you should create an actual window, and then JDK will use that window for creating an embedded frame inside it.
This is done with WEmbeddedFrame, that is derivative of an EmbeddedFrame class. I don't know exact details, though, since this classes are sun.awt, and actually sun.awt.<platform>