grub

GNU GRUB is a Multiboot boot loader. It was derived from GRUB, the GRand Unified Bootloader

Change boot order on Ubuntu 10.04

Check the Ubuntu version with lsb_release -a
Check the number of existing entries running update-grub
Count the number of entries found
Edit the file /etc/default/grub and change the parameter GRUB_DEFAULT=X, where X is the entry number desired to be the default one
Run again update-grub to update /boot/grub/grub.cfg