You know those character boxes where they show your character's face next to your health bar within the main game window. How would I make those?
Personally I'd have a look at the ImposterNode.
There is also a test in the class jmetest.renderer.TestImposterNode
You mean an animated character head? Then something with render to texture, as seen in ImposterNode, would indeed be a good idea.
But you'd have to give fenggui access to the texture rendered from jME - that might be tricky. I never tried.
I just use pre-rendered images and load them from fenggui. It's no fancy animated head, only a static image, but very easy to do. If you need help with that, I can look it up in my own project's sourcecode.
You'd probably need to render the character to an offscreen surface (FBO/Pbuffer) and then read the pixels back to a BufferedImage to send to FengGUI. It might be possible to bind a fenggui image directly by giving it a texture ID… There are many ways to do it but all of them will require rendering the character to an offscreen surface and then manipulating the result in some way.