First of all, you should find handle of the window, which are the desktop. And after that, you may work with it like with any other window.
// Hide icons on the Desktop
procedure TForm1.Button2Click(Sender: TObject);
begin
ShowWindow(DesktopListViewHandle, SW_HIDE);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
DesktopListViewHandle:=FindWindow('ProgMan', nil);
DesktopListViewHandle:=GetWindow(DesktopListViewHandle, GW_CHILD);
DesktopListViewHandle:=GetWindow(DesktopListViewHandle, GW_CHILD);
end;
// Show icons on the Desktop
procedure TForm1.Button1Click(Sender: TObject);
begin
ShowWindow(DesktopListViewHandle, SW_SHOW);
end;