The last patch that was for Civ 3 was 1.22 for Conquests, back in 2004. Nothing has been released since then. Civ 3 really doesn't need to use both cores, it's not a very hardware demanding game (it came out in 2001, Conquests in 2003). I would assume that the OS would automatically delegate tasks to the cores though - run Civ 3 on one core, and run the OS, services, and background tasks on the other core. I have a dual core system, and there really is no difference, except when you are playing with 31 civs on a huge map - between turn times go from ~2 mins to about 20-30 seconds.
EDIT (adding stuff): If the game isn't programmed to use multi cores, the OS will decided how to best handle it. Multiple cores will definately improve performance, but not as much as if the game were specifically made to take advantage of multi core systems. So getting a quad-core system will probably improve your Civ 3 performance, and let you multitask and use more software at the same time, but don't expect miracles.