5970 on the way, would like recommendations (first timer)

[btc_artist]

This particular mainboard only has one PCI-e slot and I'll only be using the box for mining. I'll boot from a USB stick, since I have no need for a HDD. I'm going to play with CPU mining litecoins at the same time as running this card, so that is the only thing that might up the wattage requirements.  The processor is an Athlon II dual core, 3GHz.

[DeathAndTaxes]

600W should be sufficient.  If you underclock the memory down to 160MHz a 5970 will only pull ~250W DC.  Overclocked CPU might pull another 150W.  400W plus a token amount for MB & fans.  You are still <75% of peak on 600W unit.

BEFORE YOU BUY A POWER SUPPLY.  Look how much wattage or amps it delivers on 12V rails.  600W is useless if it is only 200W in on 12V rail.

Newegg has links to manufacturer product page.  Look there for wattage on the 12V rail(s).  For mining that is really all you are concerned with.