While the graphics are differnt type with FPS games, HOI 2 is 2D and 2D in a huge way. Boards now have all kinds of acceleration for 3D.
This sounds like a memory issue. Since there is a lot less to keep track of in the start of a campaign, you probably do not have any trouble with the battle scenarios either.
However a Gig should be more than suffcient, unless it is not configured properly.
The first thing you may want to do is look through jpd's excellent FAQ it is written for Victoria but applies here as well. http://forum.paradoxplaza.com/forum/showthread.php?t=147392
This sounds like a memory issue. Since there is a lot less to keep track of in the start of a campaign, you probably do not have any trouble with the battle scenarios either.
However a Gig should be more than suffcient, unless it is not configured properly.
The first thing you may want to do is look through jpd's excellent FAQ it is written for Victoria but applies here as well. http://forum.paradoxplaza.com/forum/showthread.php?t=147392