I'm sure someone else already found this but RIM tech supp. couldn't answer the question. I managed to play with my 9700 and got the "today" layout on my phone by accident (and wanted Zen back). I then called my carrier who said I must have download a new new theme. I said NO...it must be a new feature of OS 5.0. They gave me a case # and RIM's phone #. Rim couldn't answer anything....
If you want the new "home screen preferences" screen and options from OS 5.0...do the following:
From you desktop screen press the blackberry button once and all your folders and other icons appear. Press the blackberry button again and a menu comes up. Choose 'option" and you are now at the Home screen preferences.
You can set your download folder peference, layout (Zen or Today), wallpaper and master reset of theme.
RIM tech support didn't even know about this!!! odd!!!