Any Live CD can restore Grub at any time.
If it has Grub then you can activate the Grub shell in a root console and tell Grub to get back to the MBR using Debian from sda7 or (hd0,6) to Grub by commands
If the Live CD has no Grub support so you can activate a Grub shell you can still restore Grub by its kernel. Again in root terminal
mount /dev/sda7 /mnt/sda7
The last one can be done on any Live CD even without the Grub support. The reason is you boot up any Linux kernel (from a Live CD) but change root to Debian. You therefore issue the grub-install command inside its Bash shell. It is a sure-fire universal method and the one to remember if you ever wish to restore grub or Lilo.
When you install XP its installer overwrites the MBR and destroys Grub's stage1 file there. The restoration of Grub is to put its stage1 back into the MBR. All the necessary files are already inside the Debian partition. The command "root" + "setup" in a Grub shell or "grub-install" in Bash shell will make the necessary connection.