And there is an updated tutorial/demo available too:
Nifty 1.2 – Updated Tutorial/Demo
The Tutorial/Demo has been greatly improved and updated with Nifty 1.2 informations and is *THE* source to learn how to use Nifty!
Please note that starting with Nifty 1.2 the main nifty.jar is now independend of lwjgl and slick2d. This means you need a nifty-<system>-renderer.jar for your rendering system! For instance, if you would like to use Nifty with a Lwjgl based rendering backend you will now need to download nifty-1.2.jar as well as nifty-lwjgl-renderer-1.0.jar!
Please note that we assume that all of the required jars of your rendering system, like lwjgl.jar, slick.jar and so on are downloaded by yourself. The nifty-<system>-renderer.jar only acts as the adapter between nifty and your rendering backend. They don’t come with all the required libs. This decision was simply done under the assumption that Nifty comes as an add on to an existing application.
The Nifty 1.2 compatible jme2 renderer will be available soon after the 1.2 release and Nifty 1.2 will be integrated into jme3 soon as well.