I have the same problem. For no apparent reason, the screen goes black except for the character windows on the upper right and the minimap on the upper left. Only happens during combat. Other DirectX games work fine. I even upgraded my graphic card drivers to the latest version (radeon 9800 pro.) I can save the game, exit the application, reload and open the game. It's getting so bad, I don't feel like playing it anymore.
While I'm here, I might as well mention the other problem, sometimes one of my characters will somehow make it to the outside walls of a dungeon, you know, the black area where nothing is supposed to be. You can walk him all around the map, tracing the outline of the area. Sometimes this happens to monsters too. I'll look for another post on this one.
John