There were two versions of the Earth map included in the Mac version of Civ 3, one is standard size, and one is huge. They can be found in the "Load Scenario" option in the main menu. From there you can set up a game just as you normally do, except now the map is set.
These world maps are not great, or not as great as they could be. Fortunately, there are many fellow players who have taken the time to make maps that are much more accurate than those that were shipped with the game. They can be found in the Downloads section on the CivFanatics main page. The files work on both the PC and the Mac versions of the games, so hopefully you should have no trouble running them. I haven't tried a whole lot of maps, but the ones I have tried work. While you are there, take a look at the other maps besides the World maps, there are quite a few that are very well done. All you have to do is download them, and then put them in the scenario folder, and load them as you would any other scenario.
Hope this helps!!!