Replying to Dual 8500GT 256mb and DX-10

Aright. I need a new computer and I am building my own. And I was wondering if I put Dual 8500GT 256mb in SLI mode that I would need 500 watts or 700 watt power. Also will this work good with vista and DX-10. Also I am putting in a AMD dual core 3800, 2 gig memory sticks, thermaltake cpu fan. I am also getting a DX-10 compatable 19" monitor.

This is everything that will be in my Computer.

TURBO X-DREAMER CASE 350 WATT W/ WINDOW & LCD Temperature