Good and bad news - the python/XML trouble I have been experiencing where gone after a reinstall of Civ/Bts/TAM.
Sadly, things only worked twice (BtS started fine, I then loaded TAM by loading the 24 civ map as custom scenario).
Then I started (had it already installed before I tested anything) Fall from Heaven 2 with the Mod-Autostart link the installer creates, and it crashed with some python errors.
Since then, nothing works any more - BtS crashes with XML errors, TAM gets the python tag errors again (if I double click a TAM map), and FfH2 is crashing with python AND XML errors.
Guess I'll have to ask the FfH2 guys what p.o.s. they have packaged up
edit:
Finally,
I have disabled XML and file caching in every INI file I could find in the Civ4 subfolders, and now things seem to work again - mostly:
I'm back to the python: enum_type tag errors again, which I wrote about a bit earlier. This is with both different 24 civ maps provided - haven't tested with map generator script, though.
edit 2 :
I loaded ambrox' 24civ map into the world builder on turn 0, removed and reapplied the starting techs for every nation, and saved as scenario files again.
If I start a new custom scenario now with the WBS, I do not get any more enum tag errors any more.
Haven't tested, though, if the game really runs flawless over the whole timespan, with all techs etc.