I get a crash on huge maps with default number of civs and city states. I have 8GB under Windows 7 64-bit. Video card is ATI Radeon HD 4350 with 512 MB. Turning all video options down does not affect it; neither does playing the DX9 version. Reducing the number to 6 civs / 6 city states seems to work, though I haven't played beyond classical era yet. I think the problem is the limited RAM available to 32-bit applications. They need to make a 64-bit version available or many people won't be able to play huge maps or the more elaborate mods.