SVG (Scalable Vector Graphics) is an open W3C standard for graphics file format and Web development language based on XML. Those image are made up of lines, curves and other “smooth” elements so when you zoom in on a SVG it stays smooth (unlike GIF, JPEG, PNG). 

Imagine you can draw some of your user interface elements in a vector drawing application like: Adobe,   InkScape (free) or Skencil (free) and convert your work into WPF XAML or Silverlight XAML. ViewerSVG  (SVG to xaml converter) is your tool.