if you don't have success with:

Window.Hide(Application.GetWndHandle());
or:
Window.Show(Application.GetWndHandle());

then it is the Screen's window handle you are needing:

Code:
local nScreenHwnd = Screen.GetProperties().WindowHandle;
Window.Hide(nScreenHwnd);
--do some stuff here
Window.Show(nScreenHwnd);
may help you out of a 'how come it does'nt work' scenario