I have installed the JWM on Ubuntu 12.04 via the Software Centre, but it doesn't work. When I choose the JWM session from LightDM, it only shows a black screen.
It worked when I had another computer with Ubuntu 11.10, where I had the same problem after the JWM installation. But once, by chance, I chose to start JWM from a Fluxbox session. And after that, i was able to start JWM also from LightDM.
But this solution does not work for me on Ubuntu 12.04. JWM never starts.