I played the game in windowed mode for the first time yesterday and in that mode the backgrounds for some windows are missing.  They simply display the white text hovering over the cloth map.  The windows effected are the one where you choose an improvement to build, and the city information window that you get to from clicking the city's medalion at the bottom of the screen.  After switching back to full screen mode the problem was not fixed.  It was also not fixed by restarting the computer.  I have an NVidia GeForce 8600 GT with the latest drivers.