I currently have an Antec Earthwatts 500W psu and and I'm wondering if that would be enough for a HD4870x2.
My system consists of 4 Sata hard drives, Q6600, 4GB Ram, 1DVD RW drive, SB xfi extreme. I don't overclock anything.
The wattage should be barely enough however I am not sure if you will have enough amps on the 12v rail. You should check what the HD4870x2 requires for the 12v rail compared to your Earthwatts power supply
Nope, the 4870x2 uses 2 8 pin connectors if I recall correctly.
Now, make sure to use 2 and 2 HDDs on the rails and DVDRW. Also, if your card doesn't turn on right away, use the molex converter to 8 pins so you use the other rail (I failed on the first try with my 4890 xD!).
The EA500 has 34A total for the 12V rail. If the 4870x2 needs 22A (and that seems rather light to me.) then you'd have 12A for everything else. The 4870x2 requires one 8pin PCIe plug, which the EA500 doesn't have. I agree with the others, I'd be looking to get a different PSU. Your to close to the limit, and lack the correct plugs.
A quality 500W PSU like the Antec Earthwatts should not have a problem sustaining 439W. Of course, when you use the calculator I recommend you set the load to 100% and use that number. You may not even approach that number unless you're running Furmark AND Prime 95 on all but one of your cores at the same time just to test the power consumption. During Gaming you will draw considerably less power than that.
Anyway, the biggest problem will be that you will of course need adapters for the 8-pin connector, which would require you to use the remaining 6-pin connector and a 6-pin to 2 molex adapter. Not an elegant solution ^_^.