When manufacturers worn you of the healthy power requirerments of an sli configuration....you can believe it.
I had to redo all the power connections in my machine to avoid a low power warning. Keep in mind that I am using an Antec 550 ps.
I would suggest this as the bare minimum. 650 and up would be better, but offcorse this would also depend on the quaility of your ps.
PC Power & Cooling's 510 power supply would have no trouble running a configuration like mine, but Im not real big on paying 200 bucks for a ps.

Thanks for the heads up Biggie. Always appreciated.

I'd check either the nVidia or AMD site to determine the best PS for SLI/Crossfire. Although even a quality build like PCP&C could run the configuration doesn't mean it should. And I'm thinking you'd need at least a 1kW PS to run the new POS DX10 cards from AMD in SLI.