Welcome to the board, Pennfarms!
May life in the Gael Serran prove fruitful and profitable!
Now, for your challenge.... it's been a bit since I've played in the Gael Serran, but it seems there's an option for software graphics mode. Have you tried that yet?
I've noticed some similar strangeness with parts of the screen going black. Gets very annoying, it does...
I'll be back in the home office on Wednesday and I'll see what else jumps up there.