Just wanted to let you all know that there seems to be a bug in the 10.5.2 update for Macs with X3100 graphics. Civ IV crashes with a divide-by-zero exception while playing, and it's very repeatable. I've had no problems with Civ under 10.5.1 before upgrading. Someone on the civfanatics forums also reports the same problem with a new MacBook Air, and the problem has been reported with Civ IV and Warlords.
Aspyr doesn't want to support Integrated Graphics at all, so it looks like it's up to Apple to find the bug....
If you play Civ IV on a machine with an X3100, you may want to skip 10.5.2!