Of course, you could get a fairly good simulation of a round world by doing the following:
Remove any unit that moved off the north or south edge of the map and allow it to reenter the map on any square of the same side they left. So if you went north directly above North America you could come down over Europe or Asia or any other point on the north pole.
Now, I think this would best be restricted to air units as I don't think (even today) any signifigant military force could cross the poles. In my opinion allowing any land unit (except maybe an `explorer') to use this option would be rather silly, but I suppose it could be a selectable option.
With this system you could really launch your nukes over the poles like the U.S. and U.S.S.R would have done.
It strikes me as clean and fairly simple without introducting any really weird shaped spaces or taxing computers with a full 3D globe.
Joe
[This message has been edited by Joe Bourque (edited April 30, 2000).]