Under one Website Maker account, you can only have one single website published at any given point in time. If you want to create another website, you would have to open another Website Maker account (under a different e-mail address). If you have the boxed version right now, you don't need another one of those. You can just quickly and easily book another account and choose one of the available rates online:
....Ralftaro is right....but the good thing is, that you can chose a free account for another site. Also I heared the rumour that the next coming release of Website Maker will include a mode to handle more than one website via one account....