Details matter.
What happens when the game crashes? Do the game's graphics go dark, or start flickering uncontrollably, or get weird lines running everywhere? Does the game suddenly exit, dumping you back to your desktop? Do you go straight to a Windows blue screen, or does the game just freeze (mouse pointer won't move, can't click anything)? Can you Alt-Tab out of the game, and then back again (or do you get a frozen screen when you do that)? Can you Ctrl-Alt-Delete to pull up the Windows Task Manager? What does it say? What are your in-game video settings? Can you post your DxDiag file (see
http://forums.civfanatics.com/showthread.php?t=379992#5)?
The more details you provide, the more likely the community can offer solutions.