Hi
Thank you for clarifying your original question. In this case, you have to create a polygon (a quad would be enough), set its texture and vertex coordinates, and use a texture. Look at Texture, TextureAttributes and GeometryArray.setTextureCoordinates().
Edit.: this example seems to be simple enough to show you how to do that:
http://www.vrupl.evl.uic.edu/oldsite/VRLabAcc/about_vrlab/java3d/lesson05/index.html