This just came up in a discussion and I figured it’s worth passing on.  With Pocket PC 2003 Second Edition, OEMs are able to build devices that are either square-only, portrait-only, or portrait/landscape-rotatable. 

To figure out if a device supports rotation, just call ChangeDisplaySettingsEx and use the CDS_TEST flag.  The screen can then be rotated with that same API.

-Robert