I ended up getting 2 copies of Civ IV and 2 copies of the expansion and plan on spiltting the savings with my friend.
We only saved $10 each, but $40 for all of Civ IV isn't bad. Thanks OP.
On a side note, this is my third order with Amazon in only three days! Madworld Pre-order, Lego Batman PS2/Persona 4 order yesterday, and now this. Jeez, I really need to stay off this website...