Is your desktop colour depth set to 16 bit? Some have had problems with their mini-map with it set to 32 bit.
Try running the configuration program and switching to software or Direct Draw mode, to see if that helps.
Try deleting all of the files in the '..\Divine Divinity\Run\Dynamic' folder.
This folder is used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied from that folder when you save a game. The files will be re-created as required the next time you start Divinity. If there was a corrupt file in that folder, deleting the files should fix the problem.
After this, try starting a new game and see if the you still have a problem with the maps.
