You mean rotating the screen 90 degrees into portrait mode? You need to go into the video card's software and change the rotation settings, manually. It won't happen automatically.
UPDATE: My bad, I checked the specs of this monitor (http://www-01.ibm.com/common/ssi/cgi-bi ... anguage=en
) and learned that there's indeed a special software that enables an automatic switch from landscape to portrait. I thought it couldn't do that, because I had looked into this monitor in depth a few years back and didn't recall reading about this feature. So, the obvious thing for you to do is to obtain this software.