The recommended requirements for that game, which are higher than minimum and usually allow high settings, are a HD4850 or GTX260, which have 512MB and 896MB.
So theoretically a 1GB VRAM GPU should work fine. Theoretically meaning IF the game is as well optimized as they claim. Keep in mind any game you buy on Steam can be fully refunded for any reason if you've played it less than 2 hrs.