Chess King with Houdini 2 and Chess King Pro with Houdini 2 Pro will always have the latest Houdini 2 version, via automatic auto-update. At the moment, the latest Houdini 2 release is the Houdini 2.0c, included  in both Chess King and Chess King Pro. The difference between the standard version and the Pro is that the Pro uses all available processors and the standard Houdini 2.0c uses only one processor (that’s still quite decent performance and recommended if the computer is not very powerful). In Chess King Pro, the Houdini 2 Pro also has a whole series of settings that can be adjusted, whereas in Houdini 2.0c standard, the engine is optimized to run with Chess King and the only settings that can be changed are the numbers of variations you want to see in the engine analysis box.