I got Civ3 from Wal-Mart and I had a lot of fun from what I played. But for whatever reason (I blame Wal-Mart, and myself by extension for shopping there), the inside ring started cracking and the disk became unusable.
I ran Civ4 Vanilla on my old ass Windows based machine. It doesn't run fantastic and it can be a pretty long wait between turns towards the end of the game. I'm not very savvy about the capability differences between PC's and Mac's, but they look pretty similar to me. You might be able to get away with running it by just upgrading your RAM.
It crashes when I try to play Beyond the Sword on it, though.
I use my Mom's laptop to play now, and I've learned a few tricks since. Playing with less players on a smaller map probably would have helped me a lot.
I've got a 1.2 Gig Processor, 1 Gig of DDR RAM and a Radeon 9250. I believe those are below the minimum system req's, I know squat about video cards, though. But your processor is better than mine, I think the vid card probably is too?
Anyhow, you can get a way cheaper copy on eBay. There are more than enough people that buy these games, reel at the depth and complexity and go back to StarCraft or whatever. Definetaly get Civ3 Complete. If you loves it, see if you can scrounge up Vanila Civ4 for cheap or try to find a less than legal copy.