Age of Ice is a Prequel to Fall From Heaven, which occurs when the Age of Ice ends and the Age of Rebirth begins. Age of Ice isn't nearly as good as FfH, but if FfH is overwhelming it may help you to start with the less complex prequel. It does contain lots of good lore too.
The FfH II is being done in stages: Light, Fire, Shadow, and Ice (not to be confused with Age of Ice), each consisting of several different releases in which more features get radded (and occasionally removed). Light and Fire were versions for Civ IV vanilla (there were also 2 BtS conversion Betas that may or may not count as Fire). The current version is Shadow, and next week's release and probably the one after that will still be Shadow too. At the end of Shadow, the mod's functionality should be complete; Ice is made entirely on Scenarios (like AoI) built on the base of Shadow (although I'm sure that if Kael realized that there is something these scenarios need that he forgot to implement he'll consider adding it).
