If you decide to make the command window horizontal, it opens up a ton of new options.
You could place it under the Status Window like I had originally mentioned, or you could place it above the Help Window as earlier stated, but you could also cascade the help and command windows to equal the full 640px. You have a lot of options.
You could even place the Help Window above the Command Window, but I wouldn't care too much for that I don't think.