The usage for dbSetCameraToFollow is (X, Y, Z, Angle, Distance, Height, Smoothing, Collison); just passing the objects id to all the paramenters is not going to work.
Your basicly telling it to track a point in 3d space and not anything in particular. To track your cube the first 4 would be dbObjectPositionX(3), dbObjectPositionY(3), dbObjectPositionZ(3), dbObjectAngleY(3). Then distance would be how far away from the point you want the camera to remain, height is pretty much the same, how high up from the point. Smoothing is a value 1-100, and collision will make sure the camera takes into acount collison.
All this information is in the GDK Help file and is very useful for finding out how to use the commands or even for just finding a command you don't know anything about.