There are some good Lilo & Grub bootloader Howtos in the Tutorial sections here, be sure to read those.
If you use Lilo as the bootloader, you would have to add it to MBR and it should pick XP as another OS to add to it during installation of Debian. Grub should pick it up also, but not sure if Grub is included with 2.2.
If you want to use NTLDR as the bootloader here is a link on how to do it.
Of course, I've never done it using two different hard drives, personally, so If something is wrong, someone else can explain better.