I've been perplexed over this problem for the past week. On previous version of windows (post-Win2k), you were able to employ the following C# code to essentially pin your window to the desktop:
IntPtr pWnd = UnsafeNativeMethods.FindWindow("Progman", null);
IntPtr tWnd = this.Handle;
where FindWindow and SetParent are imported from User32.dll. The window would essentially be part of the desktop background, no other window could hide behind it and when you click show desktop, it would still be on screen. On Vista, this does not work when DWM is enabled. The code does not throw any exceptions, it's just not visible. Does anyone have any idea how to do this on Vista with DWM enabled?