My current computer is pretty nice, not gonna bother listing off all the specs but having a 500 watt power supply has worked perfectly with a good video card, 2 gigs of ram, 2 HDDs, etc.
I'm building a new one that has dual Radeon HD 3870s 512mbs, 4 gigs of ram (two OCZ Reaper sticks of 2gb each, 240 pin DDR2 1066), an ASUS M3A32-MVP Deluxe AM2/AMD 790FX ATX mobo, a 150g 10,000RPM WD Raptor HDD, your typical CD/DVD burner, a G5 mouse and a standard keyboard, along with a Creative XtremeGamer sound card, and a AMD Athlon 64 X2 6400+ Dual Core Processor.
It's going in this case:
The power supply I ordered said it was CrossFire ready and such, and is 750watt. I was looking at the same cards on an AlienWare computer earlier today to compare how much money I was saving and it said you had to have a 1000watt power supply to run them. Now I'm nervous cause my order has already been shipped. Anyone know how much power I'd be needing?