Using Linux Mint 8 (64-bit) dual-booting with WinXP. My wife likes XP and I like Linux.
The grub2 default boot is to Mint. To maintain domestic tranquillity, I needed the default to be XP. Searched for the solution but did not find it in this forum or others.
Solution: Open etc/default/grub with gedit or another editor. E.g., "sudo gedit etc/default/grub"
Change "default=0" to "default=5" and save the file.
Run "sudo update-grub" in a terminal.
Exit, reboot, and the XP option should be the default.
If you want other operating systems
If you have multiple operating systems in the grub menu, count the lines from the first one and use that instead of the 5 above.