I don't know whats up with this. I am using IrfanView, and I've replaced the UN in the pyramids space (in both files). When I play the game there is a black box for all the buildings.

IrfanView works with pcx files, is Civ just that touchy? I have Civ PTW 1.27.

sounds you like you accidentally promoted the colours to 16 million and forgot to turn it back down to 256