changing screen size

Hello, Using SAX2, I can't get the screen size to change from 800x600. In windows the res' is 1200x800 @ 60Hz. The device is a Toshiba laptop with the 15.4" wide screen and an Intel mobile 915GM video card. Also, not sure which Modeline Algorithm to use nor display size settings (in mm) under the expert tab. Any help would be greatly appreciated. Thanks in advance. James