All of the outdoor environments and character models look fine throughout the game world, but in every single interior space(including the caves and mines) the walls of the interior space do not render properly. I have looked all over gothic forums and haven't seen anyone come across this issue. Any ideas?

Post a screen shot that details what you are talking about and a DXdiag please.

Try the following if you haven't already:
1. Check that you have the latest video card drivers (, [url=http://www.nvidia.com/page/drivers.html]NVIDIA, etc.)
2. Update DirectX using the DirectX End-User Runtime Web Installer. It will automatically install any files you are missing.
3. Finally, try reinstalling the game.