portrait mode how to

Hi,

I am working on X11R6.8.2. Just trying to explore if there is any posibility
to put screen in portrait mode. I know about Nvidia driver. but i want to
try it by myself.

any hints how to put screen in 786x1024 mode (take the example of Intel
card). I don;t need icon rotation and all. but just want to set the mode as
768x1024.

regards,
Puneet