Problem solved. If anyone needs a quick, easy way to run Xywrite on a Mac, Boxer, a gaming program available free at http://boxerapp.com/ seems to work and is a cinch to install. Once I dealt with some directory confusion, I just dragged my "dos" folder which contained my xy4 directory and subdirectories into the Boxer "box". Then everything worked. The nice part is that the window can be resized by clicking and dragging. And it doesn't crash in full screen.