Hello Senior and experienced members of the forum

I want to setup scrypt mining rig. My hardware is:

Asus P45 Maximus Formula II motherboard
Intel Intel® Dual-Core Processor E5200
2x 6990s and 1x HD 7950
Thermaltake Toughpower 1200W Power Supply - TP-1200M  --- Would this be enough to power those graphic cards?
4GB DDR2 Ram
Normal HDD
2x x16 risers on which both 6990s would be installed and 1 x1tox16 riser on which 7950 would be installed.

Now the real problem. Would i be able to run this graphic card setup on windows 8? As i have read somewhere windows 8 allows you to run extra graphic card. I dont want to go to linux i am a noob already linux would be hell.
Is my harware choice correct? Or should i invest in other graphic card like 3x 7950. I am getting hd 6990 for around $330 which i think is a bargain.
Would i be able to run the cards successfully or am i missing something here?

Please reply urgently i want to build this rig todayyy