Well, the Athlon 64 2000+ (1GHz at 0.9v) paired with a AMD780 chipset consumes less power than the whole atom mobo itself, the CPU still consumes more than the Atom 230, it's 8w for the 2000+ versus the 4w of the 230, but the 780G consumes less than the D945, nearly half IIRC. But the downside is that pairing the 2000+ and a mITX AMD mobo is more than twice the price, doesn't make up for the around 5w less consumption. It also can outperform the 230 in some aspects.
EDIT: It also has the same core as the Athlon 1640b @ 2.7GHz, in theory you could use one and downclock it to match the 2000+ (Both "Lima Core)
There is another Atom motherboard that I am aware of, its basically the same but it has an Atom 330 which is a dual core version of the 230, exactly same clock frequency. But it also consumes a bit more since its a dual core, its model is the D945GCLF2. You have Celeron 220 based mITX motherboards that perform similarly to the Atom motherboards.
For a file server, imho, it would be a waste of money to buy a dual core version.
EDIT: Just found thisEdited by Dragoon - 10/30/08 at 7:24am