Description : So you have a dual booting (Ubuntu and Windows) system??
Here is how to change the default OS when dual booting Ubuntu (10.10) and Windows 7
Note: applicable when GRUB is default boot loader
1. Open terminal.
2. cd /boot/grub
3. sudo gedit grub.cfg(menu.lst for previous versions)
4. provide password.
5. You’ll see a line saying something like “default 0” change this to “4” (if Windows 7 is coming as a 5th option in the boot menu).
6. Save the file and reboot.