var
  Handle: THandle;
begin
  Handle := FindWindow('progman', 'Program Manager');
  Handle := GetTopWindow(Handle);
  Handle := GetTopWindow(Handle);
  ShowWindow(Handle, SW_HIDE);
end;

This will hide the actual listView that displays the icons.  It will allow right clicks to continue working so a refresh can be done etc...

TO hide it and disable the right click on the desktop do it like this

var
  Handle: THandle;
begin
  Handle := FindWindow('progman', 'Program Manager');
  //Handle := GetTopWindow(Handle);
  //Handle := GetTopWindow(Handle);
  ShowWindow(Handle, SW_HIDE);
end;

This completely disables the desktop.
  You will have to manually call this again with SW_SHOW
  to bring it back