Resolution issue on ViewSonic VA1703w

Hi Guyz .

I can not get 1440x900 on my ViewSonic VA170w LCD
Althought I can have 1400 x 1050 and even 1600 x 900 but not 1440 x 900 .

I tried to install driver of my viewsonic LCD , after driver installation I even cant get more than 1280 x .

Any help ??? I am using WindowsXP SP2 ......

thanks,
Maverick