These are the official recommended power requirements based on your graphics card:
450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode)
This applies to the entire system not just your graphics card.
The Antec Earthwatts are a very good line of PSU and have a reputation for providing high quality power supplies. You should be fine with that PSU. Best of luck!