What you could do is to open a full-screen window and apply the DWM glass effect on it, but unfortunately this stopped working in Windows 8.
http://stackoverflow.com/questions/993249/net-glass-effect-in-c-sharp-2-0-applications[
^]
Other than that, the solution is to do the gaussian blur effect yourself, which is a really CPU- or GPU-intensive task.
I have to ask: Why would you want this annoying effect? It really breaks the user experience of the user's desktop. Always remember that yours is not the only app running on the user's computer!