Current draw can be upto 3.5x running current for certain components (HD's / or optical drives are a great example).
Your PC will likely draw approx 50% more power at startup than running, over the entire system.
So you really need a power supply that can supply 400W for several seconds.
but 1000W is a nightmare ... here in oz that's 3Amps sustained .. in the US 6Amps .... just think of the losses ... power dissipated into the environment as heat ...
Also, donn't forget that PSU's can dissipate upto an extra 20% on top of what you actually use in the system....
That's a whopping potential 1200W (5A au/eur or 10A usa) dissipated overall!
Prevent the ICE age! Upgrade your PSU to an enermax galaxy 1000Wl!