Windows 7 And Crossfire

My system

22'' Asus Screen
intel Q8300 pro.
4 gb ram
ati 4650 DDR2
2 terabyte hdd
O/S = Windows 7 ultimate 32 bit

my problem ;

When i run crossfire, crosfire start in window mode (1024*768 ) but my screen reso.
1680x1050. how can run crossfire full screen ?

this problem only on windows 7 same system my second computer O/S Windows Vista i can play fullscreen

how can i fix or z8games publish any fix ?