For example, will Total Realism work for my old-fashioned, unexpanded copy of Civ, even though it says "(Warlords)" right in the thread title?

This may be a stupid question (in which case beep beep I'm a jeep dur hur), but my experience with computer games and mods is limited.

Yeah, both expansion packs add a lot of content to the game, so if a mod is made for warlords, you'll need warlords to use it.

You need Warlords for Warlords mods and BtS for BtS mods... though most of the "good" mods are either for, or have migrated to BtS... I don't see much of a need for anyone with only Vanilla Civ4 to purchase Warlords at this time... since BtS is fully-featured, has all the content of Warlords (minus scenarios) and is what 95% of the Civ4 modders make mods for.

You need Warlords for Warlords mods and BtS for BtS mods... though most of the "good" mods are either for, or have migrated to BtS... I don't see much of a need for anyone with only Vanilla Civ4 to purchase Warlords at this time... since BtS is fully-featured, has all the content of Warlords (minus scenarios) and is what 95% of the Civ4 modders make mods for.

That is, unless you are very impatient and want to play some specific mod or scenario which hasn't been converted to BtS yet!