You can go here:
http://civ2.sidgames.com
There you can find an extensive document about this topic (which I wrote).
But more importantly, I also have an application which allows you to change them (made by Rune Berge).
This question has been answered before... Although lots of people have asked this question, nobody ever seems to use it.
It's just not worth it, changing any graphics I guess. The only thing you would get is even larger archives for scenarios, while it's not all that big an improvement.
And there are only two ways of including the new graphics:
1. Include the entire *.dll (that's where the images are stored) and the only interesting files are well over 1 MB.
2. Include just the images and explain to people what they should do to replace it (with that application of Rune).
In short: Nevermind that graphics, it's not worth it. You could fiddle around for yourself a little. But after a while the fun is over, and you'll decide not to do anything with it anyway.
