CPU doesn´t really change, also memory. But it is interesting that GPU usage changes quite a lot and there seemed to even be a spike of 100% when I had the CTD. Good hint, I will explore further...
Added: OK, there is a spike of GPU 3D that goes to 100% but I am not sure if this happen with the CTD or shortly afterwards. I will try to change the graphics setting inside Civ 4 and see whether that changes anything.
2nd edit: I have chnaged the graphics settings to low, turned the Graphics Paging and the Viewports on and off and nothing helped. Still getting these CTDs when switching city views a number of times from one city to the other