hmm, I guess I should've been more specific.
Originally, the only xml files I had in my mod folder was the civilizationinfos and the leaderheadinfos, and it worked fine. Then once I started messing around with units, I figured I could do the same thing, and just put the unitinfos xml in my mod folder. When that didn't work, I put ALL of the unit xml files (from the BTS and original Civ folders) in my mod folder, and then it worked.
I'm going to work on unique buildings next. Is it basically the same thing as adding unique units? Or is there something special I have to do for buildings?