if you double click in the slightly darker bar that should do it.
i think it's great that you can customise the workspace, but it's not exactly intuitive how everything works. i've had to reset the workspace several time because i couldn't work out how to put something right.
i's probably a good precaution, once you have everything how you would lie it to save your work space, that way if you mess it up, or ever have to reset PSP you can just go straight back.