Damn this modding thing - after trying about 3 different times and 3 different ways to add a civilization (including taking one from the finished civs forum and just plugging in my own information), I've reached the end of my tether.

This seems impossible to me - how can it be this hard to do?

The first thing you have to do is edit the CIV4CivilizationInfos.xml, found in the Assets/XML/Civilizations folder.

Just copy all the <tags> from one of the origional civs, paste it after the last civ (Spain I believe), and then replace all mentions of the copied civ's name with the name of the Civ you are adding.

Then go into the CIV4GameTextInfos_Objects.xml file (in the Text folder) and add <tags> for the civ you added. Do the same as you did in the last file; just copy the entries already there for other civs, paste them, and rename them to your civ.

There are two very good tutorials in the Tutorials section. Both of whom really helped me out my with my first civ. After you make a few it becomes second nature and no problem at all. Don't give up! :)