Here's a temporary solution on how to solve the "Dark" map problem.
find the following XML file in your default install location - ..\Firaxis Games\Sid Meier's Civilization 4\Assets\XML\Technologies\CIV4TechInfos.xml
Now EDIT that XML file the file and replace all <bMapVisible>0</bMapVisible> to <bMapVisible>1</bMapVisible> - you can do this with notepad.
this will mark the map as explored, but at least now you can somewhat enjoy the game.
hope it helps.
find the following XML file in your default install location - ..\Firaxis Games\Sid Meier's Civilization 4\Assets\XML\Technologies\CIV4TechInfos.xml
Now EDIT that XML file the file and replace all <bMapVisible>0</bMapVisible> to <bMapVisible>1</bMapVisible> - you can do this with notepad.
this will mark the map as explored, but at least now you can somewhat enjoy the game.
hope it helps.