After struggling to keep this game running longer than 20 mins before inevitably CTD in the Modern era I have hit on a solution which is keeping my NVidia GeForce FX5700 running smoothly and at maximum game resolution.
Run the game in a Non-Maximised window. You can do this by editing the full screen option in the Civ4.ini file in the My Documents folder. Set fullscreen = 0.
For some reason if the window is maximised the game becomes totally unstable again, so don't double click that maximise box
Oh and if you need to stop the wonder movies stuttering, turn off anti-aliasing.
Hope some of this works for others too.
Run the game in a Non-Maximised window. You can do this by editing the full screen option in the Civ4.ini file in the My Documents folder. Set fullscreen = 0.
For some reason if the window is maximised the game becomes totally unstable again, so don't double click that maximise box

Oh and if you need to stop the wonder movies stuttering, turn off anti-aliasing.
Hope some of this works for others too.