Landscape mode is arranging three displays arranged all in a row. 3D Vision Surround and Surround (2D) both support Landscape mode.
Portrait mode is arranging three displays rotated either 90 degrees clockwise or counterclockwise. Surround (2D) supports portrait mode. 3D Vision-Ready LCDs do not support portrait mode. However, you can run 3D Vision Surround with 3D projectors in portrait mode.