Xdriver window resizing

Hi,
is there a quick way of resizing an Xdriver window to the exact size
of a raster, so that there is no "background" behind the displayed image.
I know you can set the size with which the window is OPENED, in the .grassrc
file, but how do you change it afterwards (other than doing it "by hand")

thanks,

                                            Andrea Giacomelli
                                        DIIAR Politecnico di Milano, Italy