Dan, I have exactly the same issue with my standard HP desktop with Windows 7 (64 bits).
I only have the issue with the map editor. The way I work around is, as I have a 24" Full-HD screen
- I select the area of the map I like to view, and it is a rather large view with the big screen
- I select a hex in the middle of the view
- Having the hex selected, I press "1", if it is the zoom-in view I want to work with,
- And the map redraws itself.
As long as I don't scroll everything is OK
- Then, I scroll to a new position, select a hex, press "1" (or what ever the view you are working with, you do not need to change it), and again the map re-draws.
This behaviour has nothing to do with the size of the map (unless, of course, the whole map fits into your screen at once, then there will be no problems).
I had a thread about this some times ago either here or at Matrix, and it seems some of the guys with W7 64 bit do not have the issue, they have no problem at all.
Now, it seems your problems are worse than mine as I do not have any issues with normal game play using that map, nor, weird enough, when I use the Scenario editor at the exactly same map.
I am afraid I can not help as to what is behind this behaviour, but I can assure you are not going mad. You might've been screwed, though
Go figure.