sli not showing in CP

Anyone know how I can enable my nvidea sli on vista, as the option is not showing in my control panel.

mobo is - Asus Striker II Extreme nForce 790i Ultra SLi (Socket 775) PCI-Express DDR3 Motherboard

Graphics cards are - 2x Asus GeForce GTX 280 1024MB GDDR3 TV-Out/Dual DVI (PCI-Express)

Thanks