Easiest way, in the edit menu, select general preferences, then in the window that pop ups select interface tab and select open to factory radio button. Now restart poser and you will be back at the default setting.

Then I would use the ui dots, normally located near the bottom left. Click on the first (empty dot) which will then fill. Now if you make any changes to the interface you can simply click on this dot to get back to the basic layout. Once you played around and found a layout you like just click on another dot to save it.