This is a common pitfall, one that almost everyone experiences at sometime. The default mode for most 3D graphics rendering pipes is to cull (i.e., not draw) surfaces that are facing away from the viewpoint. Often this dumb strategy works and pays off well in performance. But when you want to view the inside AND outside of an object, the method is problematic. You can either export your object using a double-sided material (I don't know for sure that blender supports this) or within Vizard disable backface culling with the <node3d>.disable command.
Here's a more detailed explanation of backface culling:
http://gpwiki.org/index.php/3D:Backface_Culling