having moved from XP to Win7, I also noticed that on map clicks are significantly delayed. Using the menus work better, maybe that's your work around, spence... (being spence's opponent I have an interest in seeing this problem solved)
Michael, does the interface use GDI+ primitives by any chance? (in this case something about the mouseover/mousedown combination on the map graphics, as crackace suggested). If so, you might want to have a look at those, because they are less and less supported since Win7 (basically, handled as code, instead of graphic card primitive calls), and some of them have become very slow on modern machines. I don't know about DirectX, but you might have the same problem with Win8.
Francois (been there, done that)