Eli asked about OpenGL, Direct Draw, and WPF, and how they work with Desktop composition...
OpenGL can go through one of three paths in Windows Vista depending on how your computer is configured.
DirectDraw works by creating shared surface and allowing you to draw to it, but if your application locks the primary for drawing, this will cause the DWM to shut down also, because the applicaiton is essentially saying "I'm a full-screen application, so give me the the whole screen to draw to, instead of whoever is currently using it".
WPF is hardware accellerated for things like text, geometrry, etc. and presents to a D3D shared surface which is the composed to the desktop by the DWM.