[Ubuntu] How-to boot windows by default

After a fresh Ubuntu install, on a Windows PC, the Grub boot loader put Linux as the default system.

To change the default OS (Windows to boot first in our case):

• edit the menu.lst file (in /boot/grub) with root rights.
  For example with the Vim editor in a shell:
  

  sudo vim /boot/grub/menu.lst

• find and change "default 0" to "default X" where X is the "position" of the Windows OS in the list presented by Grub at boot time (count the "title"s/lines beginning with X=0 for the first line)