Easy - you go to the Civilization 4 file in Documents, go to the mod folder, copy Earth 18 civs and Earth 1000 AD and paste it in the Civilization 4 Warlords - Mods folder. All mods are forward compatible, if there are no XML changes, which there aren't in either of the mods.
EDIT: I was wrong - the scenarios should be in the Public Maps folder in the Civilization IV file in My Games. You need to copy the Earth.Civ4WorldBuilderSave and Earth1000AD.Civ4WorldBuilderSave files in there.