get plot in a window when running R in the shell

however I want the plots to appear in a window (as it happens when the
code is run interactively) instead of being saved in 'Rplots.ps'. Is
that doable?

You could explicitly startup an X11 graphics device before your first 
plot in your R source code, something like:

  x11()
  hist(runif(100))

Works for me, although the window will disappear very quickly unless the 
script pauses before ending!

Baz