The demo contains two levels from the game, one where you play at Jack Driscol and another where you play as Kong himself and get to fight a lot of dinosaurs. As with most PC demos these days it is on the large size at 300mb and will probably last no more than 30 minutes, but does give you an idea of what to expect from the game. King Kong is released on all platforms in November (We assume December for the Xbox 360 version).

You can get a list of download locations here as well as detailed information on recommended system requirements to run the demo.