Win xp vs sapphire radeon 4870 x2

Greeting;

i bought the sapphire radeon 4870x2 and i install on asus p5q3 deluxe.
the last ccc from ati 9.3 installled
windows xp 32bit and 64bit installed.
but still the second gpu disabled on both OS.

i tried on vista 32bit still the same problem
but on vista 64bit it shows seconed gpu linked.

so is the graphic card not comppatable with xp versions??

thank you.

my spec:

mobo: asus p5q3 deluxe
cpu: intel core 2 quad 9550
vga: sapphire radeon HD 4870x2.
RAM: ocz fatal1ty 2x2GB DDR3
PSU: ThermalTake 850w
HDD: 2x 500GB WDD 7500rpm
case : ThermalTake Armore w/25cm side fan, self modefied with 8 fans.
Cooling CPU: Thermal Take solution.
OS: xp32, Xp64, Vista 64.