I don't think it's your graphics card causing all of this, although it may cause some of it, at least the lockups when fighting battles. Have you checked the Windows event log for any information the OS may have logged about crashes in the drivers? Back when I had a crappy Nvidia card, I had to use drivers that were over a year old for any Direct3D game to work at all, and then it ran... Well, sluggish would be too nice a word. You could try various driver versions and see how they work.

That crash when loading the campaign map after a battle though happens to many others too, so I don't think this is the display card screwing up. I have no idea how to fix this, beyond what is listed in the frequent issues that is, but you knew those already. If anyone knows what we could have screwed up for that to occur, please post.