How can I set the window size of a plot window?

Is it possible to set the window size / position of a plot window (figure)?

plot(0:20, sin(0:20))

Or is there any other possibility to change the size of the print() command?

print('aa.png', '-dpng')

Because the -Sxsize,ysize parameter doesn't change anything. The size of the written picture (aa.png) has always the same size as the plot window.

I'm using Octave 3.0.