By default, when you run Crysis in Windows Vista on DX10-capable hardware, it will automatically run in DirectX10 mode, whereas Windows XP can only run in DirectX9 mode. You can see what mode the game is running in at any time by using the r_DisplayInfo 1 command. While you can't force DX10 in XP, you can force DX9 mode in Vista, and this can provide a significant performance improvement for a barely-noticeable decline in image quality. To do this, right-click on the Crysis launch icon in Vista's Games Explorer and select 'PlayDX9 ', or right-click on the game's desktop launch icon, select Properties, and in the Target box one blank space after the last character add -dx9.
