I got an Geforce 7900 GTO and got same corrupted graphics, I have the latest Nvdia drivers.
It looks something like the screenshot in this thread http://forums.demigodthegame.com/346258/
Suggestions there did not help.
When it happens you can hardly see anything, sometimes when you zoom in or out it gets a bit better and sometimes even dissappears for a small time.
I played around with settings no luck.
I downloaded Ati tray tools but as i suspected it gave me the message i don't have an ATI card.
With the nividia control panel there is no geometry instancing option.. Also tried Rivatuner, which also didn't have it.
What can I do to fix the graphics?