You should design and test your application for a range of pixel densities, for both portrait and landscape modes. Systems typically support pixel densities of approximately 96 dots per inch (dpi). Many Tablet PCs ship with pixel densities of 120 dpi or greater. Ensure that your application renders text and graphics properly on higher density display devices. In particular, avoid controls and windows that are not dynamically sized according to the pixel density and bitmaps that are drawn with the BitBlt() method.
You can test your application without a high-density display. In Control Panel, click the Display icon and, on the Settings tab, click Advanced. On the General tab under Display, you can adjust the DPI setting to any level.
For a thorough introduction to the details of developing for high dpi, see How to Write High DPI Applications on the MSDN® Web site.