Did anyone figure out a fix for this? I just installed a Radeon 9800 card and now the same thing happens to me. I can't run the game in full screen or windowed mode. I've tried the 3.8 and 3.9 drivers, as well as those Omega drivers someone linked in the sticky thread, but nothing.
I've actually stopped playing the Dominions_II demo because it's painful for the game to end at turn_40. I wish the developers didn't do that. So I've decided to just wait until my full Version arrives.