If all you are looking for is a standard glass effect (which includes blurring), check out this article:
http://www.codeproject.com/KB/vista/AeroGlassForms.aspx
Basically, all you do is expand the window frame (which already has a glass effect) into the client area. You must call the DWM API that ships with Windows Vista or later using a couple of P / invoke methods because it is not built into the .NET Framework.
EDIT: , DwmEnableBlurBehindWindow DWM API, .