Oh Dear. This is the same problem I had when I bought an OCZ 500 watt PSU.
This is gonna suck, but as far as I know the only way around it is to buy another PSU with the 8 pin CPU - there is not enough power going to the motherboard to boot up, even with the 24Pin ATX.
This is why my new PC is still not running - I need a PSU with an 8 Pin CPU too.
Edit:// You should have at least a 4 Pin you can plug in, sometimes you get lucky and it will run off that. If that doesn't work - im afraid you need the full 8 Pin.
Edit 2:// 8pin CPU +12V - That is the proper name for the plug you will probably need.
Personally i would drop one of the Graphic Cards and get 4GB of Ram instead.
In newer games such as Cryisis you can find quite a performance game with the extra memory and also if you plan on using Vista, it makes the whole experience a little bit better (eg that memory hogging part of Vista called Superfetch!).
The whole point of the "Black Edition" is that the multiplier is unlocked and you don't have to adjust voltages etc unless you want a very high overclock.
For example i have an AMD Athlon X2 5000+ "Black Edition" and by simply pushing the multiplier up to 15, i can get a stable 3.0Ghz speed from 2.6Ghz without having touched anything else (Obvioulsy i have a big aftermarket cooler too).
But if i want to go past 3.0Ghz, then i would have to adjust voltages etc as the system will start to become unstable due to the multiplier being pushed up too high.
I have a Black Edition X2 in my new PC and all you have to do is enter your Bios and manually adjust the multiplier - you do not have to touch voltages etc.