An 8400GS would run the game, but you could get something better for only a fraction more money. If you're on a low budget and have a "weaker" power supply, I'd suggest an ATI 4650 or 4670. Good lower resolution gaming performance, low cost, and low power consumption all packed into one.
Can you post some specs? Motherboard & Power Supply make/model, CPU, and what additional devices (drives, sound card, USB, etc) you're using, as well as what resolution monitor you have? It would make recommending a card that's completely compatible with your system and would compliment it well much easier.