Here is a little trick that you can do to change the screen orientation in Windows XP.
Hold down the Ctrl + Alt keys and press any of the arrow keys. The screen will re-orient to match the arrow key that you pressed as shown in the image below.
A few practical uses I can think of for using this trick is: change the orientation from landscape to portrait while using a Tablet PC or, if you want to see an image in a different orientation but can’t change the orientation in the application. Maybe you can think of other ways of using it.
You could also use this trick to just play a prank on your unsuspecting co-worker by changing the orientation on his/her computer. Of course the prank would work only if he is not already aware of this trick.
Update: I am told that this hotkey works equally well in Windows Vista. But I have not been able to confirm it since I don’t use Vista. If any of the readers can confirm it or otherwise in the comments, it would be great.