Hello
I showed on 22. in Berlin a VR installation (but not Cave, just one screen and footcontrolled input) done with another open source free software called Blender
Its a 3D modelling and animation package which includes a Realtime Engine which also can save standalone applications, is scriptable with Python and can do Stereorendering:
http://www.blender3d.org/cms/Game_engine.487.0.html
Cheers,
Malte Steiner media art + development -www.block4.com-