.
[Delphi]
procedure ShowDesktopIcon( const YesNo : boolean );
var h : THandle;
begin
h := FindWindow('ProgMan', nil);
h := GetWindow(h, GW_CHILD);
if YesNo = True then
   ShowWindow(h, SW_SHOW)
else
   ShowWindow(h, SW_HIDE);
end;

-------------------------------------------------------------------------------
[C++ builder]
void ShowDesktopIcon( const bool Show )
{
  HWND h;
  h = FindWindow( "ProgMan", NULL );
  h = GetWindow( h, GW_CHILD );

  if ( Show == TRUE )
     ShowWindow( h, SW_SHOW );
  else
     ShowWindow( h, SW_HIDE );
}

void __fastcall TForm1::Button1Click(TObject *Sender)
{
  static bool Showing;

  Showing = ! Showing;
  ShowDesktopIcon( Showing );
}