You will have 30 opponents. You will want to pick the Huge map which will be a randomly-generated 250x250 map in this scenario. The tech rate has been slowed, some naval unit movements have been modified, and the OCN is set to 28.
They designed this for all-war succession games which is the reason for slowing the tech rate. It might make for a slower single-player epic game.
Unzip the biq to your .../CivilazationIII/Conquests/Scenarios directory.
Start game by choosing Civ-Content on startup screen. Find the AWvs30civs (250X250).biq entry and proceed from there.
Matt_G attached this to a post in July 2008, but I think it belongs here, too.
Text from the readme.txt in the zip file inside spoiler tag:
31 Civ Random 250x250 Huge Epic Map 2016-10-05
31 Civ Random 250x250 Huge Epic Map