I have the same problems listed as others here. I have tried installing SketchyPhysics 3.2 (which lists as 3.1), and had limited success with attempts to connect joints, usually with a message in the top left "Requires SketchyPhysics 3.2". I have also tried uninstalling and then installing SketchyPhysics 3.1, which comes up with the message "Requires SketchyPhysics 3.1". Without the ability to connect my hinge joints, the model does not simulate correctly. I have had some intermittent success with more basic sketchup models, but usually encounter the same issue. I have been following the steps as per the tutorials etc exactly, and experimented around with different state and shape combinations. I am using the latest Sketchup 8 which I downloaded less than a week ago. This problem is occurring on both Windows 7 Ultimate and Windows XP Professional installs.