What ever the specs of a laptop you have to half it, due to it being smaller and using less power.
Does your friends laptop have a graphics card thats not sharing RAM?
I understand the problem you are having as i used to try and play on a laptop, and even older games would soon over heat it.
But if it is a power house laptop, it could simply be civ 4 having memory problems or other issues making it CTDT. from some other threads i hear civ 4 is having some running problems...