Although the system requirements state that the game requires 512MB of VRAM, I've found that the demo runs perfectly well on my MacBook Air, which has only 384MB of VRAM. (Graphics card is Intel HD3000).

You'll find that this is the case for a lot of games. Minimum requirements tend to be a bit higher than are actually required, to prevent people on weaker computers from buying games they can barely run and then complaining about bad performance.