Well, actually... or... uhm...
Some parts of Civilization AGA is packed (with some version of PowerPacker, if I am not misstaken, because when wanting to edit the graphic files, for example, one has to unpack them first)...
...on my Blizzard 1230 the game ran perfectly fine for me, from disk and from harddrive, with or without WHDLoad. But on my Blizzard 1260 I've had exactly the same problem as you describe... a green screen as soon as try to run the game from HD (but from disk works just fine).
I'm not sure, but I think I've read somewhere that this is due to the PowerPacked files (or whatever kind of way the files are packed). But I may be way off here...
...besides, the WHDLoad slave should handle this anyways, I am pretty sure (but it doesn't say anything in the WHDLoad installer readme, though)...
