Note: I'm pretty sure that the source of my problems is a messed up Civ4 installation due to an OS switch without reinstalling the game. I'm describing the problem anyway in case somebody runs across the same thing later and comes here looking for help, also there's the odd chance that someone recognizes this specific problem and can give me specific instructions.
I downloaded v1.01c of this mod and tried to install it, but ran into a problem. Nearly at the end of the installation, an error message pops up, reading "Error opening file for writing: \Mods\Better BUG AI\UserSettings\Adv Unit Naming.ini". I then get the option to abort, retry, or ignore.
A quick check of the files that got installed up to this point reveals that there is no "UserSettings" folder in my "Better BUG AI" folder. Manually creating a "UserSettings" folder and retrying the operation does not change the error though.
I can, however, open the installer with 7zip and manually copy the file "Adv Unit Naming.ini" into a manually created "UserSettings" folder.
The situation is the same for the "CustomDomAdv" folder and all files contained in it.
There is enough space on the drive and I don't see any issues with access rights. I'm on WinXP and logged in as an admin.
In case it matters, the installer also noted a lack of any registry keys when trying to automatically find file locations - probably caused by me installing the game on Win2K and now using it on WinXP.
Starting the mod leads to an immediate crash. Starting the unmodded game works. Interestingly, the game itself says it's at version 3.19, although I know for sure that I installed the latest patch. I haven't played Civ4 in a while though, so I may miss or misremember something. I tried reinstalling the 3.19 patch, but the patch installer won't start, it complains about "Civ4 not beings installed properly".
I'll reinstall Civ4 and see whether that solves the problem.