Can you post a dwg file, we can't see settings from a screenshot. First, you are using the Mac version and I have no idea how that differs with Windows so some advice may be incorrect, however, how are you creating the viewport? and how is your paper layout setup, in Windows at least you right click on the layout tab and select "page setup manager" or you can type the command "page setup" from there choose modify and that will bring up a dialogue box with all the settings for that layout, it should be here that you select the paper sizes and orientation etc.
If that is correct then what units are you using in the drawing area "-dwgunits" command, this goes through a series of default values, make a note of those values and post back (pressing enter each time accepts the default and gives the next value).
Are you drawing in Model space using real units so when you draw a line of 50mm you use 50 as the length, forget the idea of scale at the moment that just confuses people.
