Appended group is invisible in game

I have just a few days experience with blender, and I’m currently working on a project where want to append certain .blend files into the main .blend file. This works, and the objects show up as a group in a certain hierarchy. When I try to enter game mode (P key) however, the appended group is not visible. I checked the transparency options, the render button in the Outliner and the renderability button in the Physics tab, but they all seem to be set up okay. When I link the object instead of appending it, it renders just fine. Any suggestions on what might be wrong here? I’m using 2.53.

A related question: Can I make these appended (or linked) objects act like regular ones in the physics engine? I tried making the (visible) linked object a Rigid Body, but it just remained immobile when it should fall (the Rigid Body cube I put next to it fell just fine).

EDIT: Fixed my first problem, it turned out some element in the hierarchy was set to the wrong layer.