On the PC (running Ubuntu 10.4) that I have interfaced to my radio gear I have the occasional need to dual boot back to XP. Here are the notes for how to get the dual boot working properly with grub 2.

Existing Ubuntu 10.4
Install XP (Grub will get overwritten by XP)

Boot Ubuntu 10.4 via a LiveCD or USB thumb drive

sudo fdisk -l
sudo mount /dev/sda1 /mnt (assumes that we are using sda)
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt
nano /etc/default/grub (make any updates that you might need)
update-grub
grub-install /dev/sda (installs grub to the MBR)
grub-install --recheck /dev/sda

Press Ctrl+D to exit out of the chroot.

sudo umount /mnt/dev
sudo umount /mnt/sys
sudo umount /mnt/proc
sudo umount /mnt

reboot

Notes from : https://wiki.ubuntu.com/Grub2